Quantum Physics
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 [1] arXiv:2406.12924 [pdf, html, other]

Title: The Noiseless Quantum Computer Does Not ExistSubjects: Quantum Physics (quantph)
In this note we show that any logic gates in a quantum computer is informationally dependent on another quantum logic gate.
 [2] arXiv:2406.12927 [pdf, other]

Title: Selfadjoint extension procedure for a singular oscillatorComments: 12 pagesSubjects: Quantum Physics (quantph)
For a singular oscillator, the Schrodinger equation is obtained an equation of eigenvalues, and the dependence of energy on the selfadjoint extension parameter is established. It is shown that the selfadjoint extension violates the wellknown property of equidistance of energy levels for the oscillatory potential, wellknown in quantum mechanics. The concept of quantum defect is generally introduced, and the wave function of the problem is written as a single function.
 [3] arXiv:2406.12939 [pdf, html, other]

Title: Measurement of ManyBody Quantum Correlations in Superconducting CircuitsComments: 12 pages, 4 figuresSubjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall); Quantum Gases (condmat.quantgas); Superconductivity (condmat.suprcon)
Recent advances in superconducting circuit technology have made the fabrication of large, customizable circuits routine. This has led to their application to areas beyond quantum information and, in particular, to their use as quantum simulators. A key challenge in this effort has been the identification of the quantum states realized by these circuits. Here, we propose a probe circuit capable of reading out manybody correlations in an analog quantum simulator. Our measurement scheme, designed for manyphoton states, exploits the nonlinearity of the Josephson junction to measure twopoint (and potentially higherorder) correlation functions of the superconducting phase operator. We demonstrate the capabilities of this design in the context of an LCladder with a quantum impurity. The proposed probe allows for the measurement of inherently quantum correlations, such as squeezing, and has the potential to significantly expand the scope of analog quantum simulations using superconducting circuits.
 [4] arXiv:2406.12973 [pdf, html, other]

Title: Tomography of clock signals using the simplest possible referenceComments: 7 pages + 10 pages appendix, 1 figureSubjects: Quantum Physics (quantph); Mathematical Physics (mathph)
We show that finite physical clocks always have wellbehaved signals, namely that every waitingtime distribution generated by a physical process on a system of finite size is guaranteed to be bounded by a decay envelope. Following this consideration, we show that one can reconstruct the distribution using only operationally available information, namely, that of the ordering of the ticks of one clock with the respect to those of another clock (which we call the reference), and that the simplest possible reference clock  a Poisson process  suffices.
 [5] arXiv:2406.12978 [pdf, other]

Title: Tensor networks for noninvertible symmetries in 3+1d and beyondComments: 72+1 pages, 11 (numbered) figures, 2 tablesSubjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel); High Energy Physics  Theory (hepth)
Tensor networks provide a natural language for noninvertible symmetries in general Hamiltonian lattice models. We use ZXdiagrams, which are tensor network presentations of quantum circuits, to define a noninvertible operator implementing the Wegner duality in 3+1d lattice $\mathbb{Z}_2$ gauge theory. The noninvertible algebra, which mixes with lattice translations, can be efficiently computed using ZXcalculus. We further deform the $\mathbb{Z}_2$ gauge theory while preserving the duality and find a model with nine exactly degenerate ground states on a torus, consistent with the LiebSchultzMattistype constraint imposed by the symmetry. Finally, we provide a ZXdiagram presentation of the noninvertible duality operators (including noninvertible parity/reflection symmetries) of generalized Ising models based on graphs, encompassing the 1+1d Ising model, the threespin Ising model, the AshkinTeller model, and the 2+1d plaquette Ising model. The mixing (or lack thereof) with spatial symmetries is understood from a unifying perspective based on graph theory.
 [6] arXiv:2406.12986 [pdf, other]

Title: Simulating spin biology using a digital quantum computer: Prospects on a nearterm quantum hardware emulatorPedro H. Alvarez, Farhan T. Chowdhury, Luke D. Smith, Trevor J. Brokowski, Clarice D. Aiello, Daniel R. Kattnig, Marcos C. de OliveiraComments: 10 pages, 9 figuresSubjects: Quantum Physics (quantph); Biological Physics (physics.bioph)
Understanding the intricate quantum spin dynamics of radical pair reactions is crucial for unraveling the underlying nature of chemical processes across diverse scientific domains. In this work, we leverage Trotterization to map coherent radical pair spin dynamics onto a digital gatebased quantum simulation. Our results demonstrated agreement between the idealized noiseless quantum circuit simulation and established master equation approaches for homogeneous radical pair recombination, identifying approximately 15 Trotter steps to be sufficient for faithfully reproducing the coupled spin dynamics of a prototypical system. By utilizing this computational technique to study the dynamics of spin systems of biological relevance, our findings underscore the potential of digital quantum simulation (DQS) of complex radical pair reactions and builds the groundwork towards more utilitarian investigations into their intricate reaction dynamics. We further investigate the effect of realistic error models on our DQS approach, and provide an upper limit for the number of Trotter steps that can currently be applied in the absence of error mitigation techniques before losing simulation accuracy to deleterious noise effects.
 [7] arXiv:2406.13026 [pdf, html, other]

Title: Polynomially restricted operator growth in dynamically integrable modelsComments: 5 pages 3 figuresSubjects: Quantum Physics (quantph); Statistical Mechanics (condmat.statmech)
We provide a framework to determine the upper bound to the complexity of a computing a given observable with respect to a Hamiltonian. By considering the Heisenberg evolution of the observable, we show that each Hamiltonian defines an equivalence relation, causing the operator space to be partitioned into equivalence classes. Any operator within a specific class never leaves its equivalence class during the evolution. We provide a method to determine the dimension of the equivalence classes and evaluate it for various models, such as the $ XY $ chain and Kitaev model on trees. Our findings reveal that the complexity of operator evolution in the $XY$ model grows from the edge to the bulk, which is physically manifested as suppressed relaxation of qubits near the boundary. Our methods are used to reveal several new cases of simulable quantum dynamics, including a $XY$$ZZ$ model which cannot be reduced to free fermions.
 [8] arXiv:2406.13028 [pdf, html, other]

Title: Symmetry Protected TwoPhoton Coherence TimeComments: 6 pages, 5 figuresSubjects: Quantum Physics (quantph)
We report the observation of symmetry protected twophoton coherence time of biphotons generated from backward spontaneous fourwave mixing in lasercooled $^{87}$Rb atoms. When biphotons are nondegenerate, nonsymmetric photonic absorption loss results in exponential decay of the temporal waveform of the twophoton joint probability amplitude, leading to shortened coherence time. In contrast, in the case of degenerate biphotons, when both paired photons propagate with the same group velocity and absorption coefficient, the twophoton coherence time, protected by spacetime symmetry, remains unaffected by medium absorptive losses. Our experimental results validate these theoretical predictions. This outcome highlights the pivotal role of symmetry in manipulating and controlling photonic quantum states.
 [9] arXiv:2406.13040 [pdf, html, other]

Title: Why quantum correlations are shockingComments: 10 pages, 1 figureSubjects: Quantum Physics (quantph)
A simple minimalist argument is given for why some correlations between quantum systems boggle our classical intuition. The argument relies on two elementary physical assumptions, and recovers the standard experimentallytestable Bell inequality in a form that applies equally well to correlations between sixsided dice and between photon polarizations. The first assumption, that measurement selection in a first lab leaves the measurement statistics in a remote lab invariant (nosignaling), has been empirically verified, and is shown to be equivalent to the existence of a joint probability distribution for quantities measured in the first lab. The observed violation of the Bell inequality is then equivalent to failure of a second assumption, that measurement selection in the remote lab leaves this joint distribution invariant. Indeed, the degree of violation lowerbounds the variation of the joint distribution. It directly follows there are just three possible physical mechanisms underlying such violations  actionatadistance (superluminality), unavoidable common factors linking measurement choice and distant properties (conspiracy), and intrinsically incompatible physical quantities (complementarity). The argument extends to all Bell inequalities, and is briefly compared with other derivations.
 [10] arXiv:2406.13042 [pdf, html, other]

Title: Longrange interactions in Weyl dense atomic arrays protected from dissipation and disorderComments: 15 pages, 6 figuresSubjects: Quantum Physics (quantph); Atomic Physics (physics.atomph); Optics (physics.optics)
Longrange interactions are a key resource in many quantum phenomena and technologies. Freespace photons mediate powerlaw interactions but lack tunability and suffer from decoherence processes due to their omnidirectional emission. Engineered dielectrics can yield tunable and coherent interactions, but typically at the expense of making them both shorterranged and sensitive to material disorder and photon loss. Here, we propose a platform that can circumvent all these limitations based on threedimensional subwavelength atomic arrays subjected to magnetic fields. Our key result is to show how to design the polaritonic bands of these atomic metamaterials to feature a pair of frequencyisolated Weyl points. These Weyl excitations can thus mediate interactions that are simultaneously longrange, due to their gapless nature; robust, due to the topological protection of Weyl points; and decoherencefree, due to their subradiant character. We demonstrate the robustness of these isolated Weyl points for a large regime of interatomic distances and magnetic field values and characterize the emergence of their corresponding Fermi arcs surface states. The latter can as well lead to twodimensional, nonreciprocal atomic interactions with no analogue in other chiral quantum optical setups.
 [11] arXiv:2406.13087 [pdf, html, other]

Title: Thermodynamics and entanglement entropy of the nonHermitian SSH modelComments: 13 pages, 9 figuresSubjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel)
Topological phase transitions are found in a variety of systems and were shown to be deeply related with a thermodynamic description through scaling relations. Here, we investigate the entanglement entropy, which is a quantity that captures the central charge of a critical model and the thermodynamics of the nonreciprocal SuSchriefferHeeger (SSH) model. Although this model has been widely studied, the thermodynamic properties reveal interesting physics not explored so far. In order to analyze the boundary effects of the model, we use Hill's thermodynamics to split the grand potential in two contributions: the extensive one, related to the bulk, and the subdivision one, related to the boundaries. Then, we derive the thermodynamic entropy for both, the edges and the bulk and the heat capacity for the bulk at the topological phase transitions. The latter is related to the central charge when the underlying theory is a conformal field theory, whereas the first reveals the resilience of the topological edge states to finite temperatures. The phase transition between phases that are adiabatically connected with the Hermitian SSH model display the wellknown behaviour of systems within the Dirac universality class, but the transition between phases with complex energies shows an unexpected critical behavior, which signals the emergence of an imaginary time crystal.
 [12] arXiv:2406.13109 [pdf, html, other]

Title: Nonhermitian Floquet perspective on high harmonic generation and above threshold ionization spectra from Photon statisticsSubjects: Quantum Physics (quantph); Chemical Physics (physics.chemph)
We present a proof based on nonhermitian Floquet theory that confirms the experimental findings of Tsatrafylis and his colleagues in 2017, demonstrating the coincidence between the high harmonic generation spectra (HGS) and the number of absorbed odd infrared (IR) photons leading to emitted extreme ultraviolet (XUV) radiation. This coincidence is achieved through postselection of the IR photons, conserving the total energy of the absorbed odd IR photons and the emitted XUV photons. Our derivation is consistent with their results and relies on our ability to compute the HGS in ultrahighintensity lasers using nonHermitian quantum mechanics (NHQM), which competes with abovethreshold ionization (ATI). Through our NHQM theoretical simulation, we identify the regimes where there is correspondence between the HHG and ATI spectra and annihilated pump photons (with postselection). Additionally, we demonstrate that the photon statistics in HHG exhibit Wignertype distributions, which reflect the quantum chaotic dynamics of electrons at the cutoff of the plateau of the HGS. We emphasize that our findings underscore a unified mechanism governing the three distinct measurements of HGS, ATI, and IR photon number distribution, none of which require the quantization of the electromagnetic field.
 [13] arXiv:2406.13196 [pdf, html, other]

Title: Quantum Generative Learning for HighResolution Medical Image GenerationSubjects: Quantum Physics (quantph); Image and Video Processing (eess.IV)
Integration of quantum computing in generative machine learning models has the potential to offer benefits such as training speedup and superior feature extraction. However, the existing quantum generative adversarial networks (QGANs) fail to generate highquality images due to their patchbased, pixelwise learning approaches. These methods capture only local details, ignoring the global structure and semantic information of images. In this work, we address these challenges by proposing a quantum image generative learning (QIGL) approach for highquality medical image generation. Our proposed quantum generator leverages variational quantum circuit approach addressing scalability issues by extracting principal components from the images instead of dividing them into patches. Additionally, we integrate the Wasserstein distance within the QIGL framework to generate a diverse set of medical samples. Through a systematic set of simulations on Xray images from knee osteoarthritis and medical MNIST datasets, our model demonstrates superior performance, achieving the lowest Fréchet Inception Distance (FID) scores compared to its classical counterpart and advanced QGAN models reported in the literature.
 [14] arXiv:2406.13198 [pdf, html, other]

Title: Singlephoton triggered quantum entanglement between two qubits or at least 2000 identical qubitsComments: 19 pages, 11 figuresSubjects: Quantum Physics (quantph)
This paper studies the effect of singlephoton light fields on quantum entanglement between two qubits and multiple identical qubits initially in a direct state. For two qubits, we first analyze the impact of the excited state's weight on singlephotontriggered entanglement, finding that excessive weight disrupts this process. We then explore how initial coherence affects entanglement, discovering that maximum initial coherence enables the single photon to achieve maximal entanglement. For multiple qubits, we similarly investigate the effects of the excited state's weight and initial coherence on entanglement control. In large qubit systems, we find that single photons cannot trigger entanglement when excitedstate weights exceed groundstate weights or when all qubits are initially in the ground state. Interestingly, single photons can still trigger entanglement between any two qubits in systems with at least 2000 qubits, with the entanglement depending on initial state parameters rather than the number of qubits.
 [15] arXiv:2406.13211 [pdf, html, other]

Title: Amplitude Amplification and Estimation using quantum kicked rotorComments: 10 pages, 9 figuresSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas)
The quantum kicked rotor had been widely used for studying quantum chaos and the physics of Anderson localization. It is shown that QKR can be used to design a quantum algorithm to perform unstructured search. This is illustrated through amplitude amplification, a generalization of Grover's search algorithm, using QKR system. Further, QKR is employed for amplitude estimation when the amplitude of the marked states is unknown. It is also shown that dynamical localization in QKR can be exploited to enhance the performance of the amplitude amplification algorithm by reducing the average runtime. The sensitivity of the success probability of unstructured search to detuning from resonance and the effects of noisy kick strengths are analyzed and the robustness of the QKR based algorithm is shown. The experimental feasibility of every component of the algorithm is discussed.
 [16] arXiv:2406.13239 [pdf, html, other]

Title: Pathentangled radiation from kinetic inductance amplifierSubjects: Quantum Physics (quantph)
Continuous variable entangled radiation, known as EinsteinPodolskyRosen (EPR) states, are spatially separated quantum states with applications ranging from quantum teleportation and communication to quantum sensing. The ability to efficiently generate and harness EPR states is vital for advancements of quantum technologies, particularly in the microwave domain. Here, we introduce a kinetic inductance quantumlimited amplifier that generates stationary pathentangled microwave radiation. Unlike traditional Josephson junction circuits, our design offers simplified fabrication and operational advantages. By generating singlemode squeezed states and distributing them to different ports of a microwave resonator, we deterministically create distributed entangled states at the output of the resonator. In addition to the experimental verification of entanglement, we present a simple theoretical model using a beamsplitter picture to describe the generation of pathentangled states in kinetic inductance superconducting circuits. This work highlights the potential of kinetic inductance parametric amplifiers, as a promising technology, for practical applications such as quantum teleportation, distributed quantum computing, and enhanced quantum sensing. Moreover, it can contribute to foundational tests of quantum mechanics and advances in nextgeneration quantum information technologies.
 [17] arXiv:2406.13290 [pdf, html, other]

Title: EPR Steering Criterion and Monogamy Relation via Correlation Matrices in Tripartite SystemsComments: 10 pages, 4 figures, comments are welcomed. Accepted by Physical Review ASubjects: Quantum Physics (quantph)
Quantum steering is considered as one of the most wellknown nonlocal phenomena in quantum mechanics. Unlike entanglement and Bell nonlocality, the asymmetry of quantum steering makes it vital for onesided deviceindependent quantum information processing. Although there has been much progress on steering detection for bipartite systems, the criterion for EPR steering in tripartite systems remains challenging and inadequate. In this paper, we firstly derive a novel and promising steering criterion for any threequbit states via correlation matrix. Furthermore, we propose the monogamy relation between the tripartite steering of system and the bipartite steering of subsystems based on the derived criterion. Finally, as illustrations, we demonstrate the performance of the steering criterion and the monogamy relation by means of several representative examples. We believe that the results and methods presented in this work could be beneficial to capture genuine multipartite steering in the near future.
 [18] arXiv:2406.13315 [pdf, html, other]

Title: Joint Wire Cutting with NonMaximally Entangled StatesComments: 33 pages, 6 figuresSubjects: Quantum Physics (quantph)
Distributed quantum computing leverages the collective power of multiple quantum devices to perform computations exceeding the capabilities of individual quantum devices. A currently studied technique to enable this distributed approach is wire cutting, which decomposes a quantum circuit into smaller subcircuits by cutting their connecting wires. These subcircuits can then be executed on distributed devices, and their results are classically combined to reconstruct the original computation's result. However, wire cutting requires additional circuit executions to preserve result accuracy, with their number growing exponentially with each cut. Thus, minimizing this sampling overhead is crucial for reducing the total execution time. Employing shared nonmaximally entangled (NME) states between distributed devices reduces this overhead for single wire cuts, moving closer to ideal teleportation with maximally entangled states. Extending this approach to jointly cutting multiple wires using NME states remained unexplored. Our paper addresses this gap by investigating the use of NME states for joint wire cuts, aiming to reduce the sampling overhead further. Our three main contributions include (i) determining the minimal sampling overhead for this scenario, (ii) analyzing the overhead when using composite NME states constructed from smaller NME states, and (iii) introducing a wire cutting technique that achieves the optimal sampling overhead with pure NME states, paving the way towards wire cutting with arbitrary NME states.
 [19] arXiv:2406.13319 [pdf, html, other]

Title: Multiparticle entanglement classification with ergotropic gapComments: 7 pages (to be published)Journalref: Phys. Rev. A, 2024Subjects: Quantum Physics (quantph)
The presence of quantum multipartite entanglement implies the existence of a thermodynamic quantity known as the ergotropic gap, which is defined as the difference between the maximal global and local extractable works from the system. We establish a direct relation between the geometric measure of entanglement and the ergotropic gaps. We show that all the marginal ergotropic gaps form a convex polytope for each class of quantum states that are equivalent under stochastic local operations and classical communication (SLOCC). We finally introduce the concept of multipartite ergotropic gap indicators and use them to present a refined criterion for classifying entanglement under SLOCC.
 [20] arXiv:2406.13338 [pdf, html, other]

Title: $su(d)$squeezing and manybody entanglement geometry in finitedimensional systemsSubjects: Quantum Physics (quantph)
Generalizing the wellknown spinsqueezing inequalities, we study the relation between squeezing of collective $N$particle $su(d)$ operators and manybody entanglement geometry in multiparticle systems. For that aim, we define the set of pseudoseparable states, which are mixtures of products of singleparticle states that lie in the $(d^21)$dimensional Bloch sphere but are not necessarily positive semidefinite. We obtain a set of necessary conditions for states of $N$ qudits to be of the above form. Any state that violates these conditions is entangled. We also define a corresponding $su(d)$squeezing parameter that can be used to detect entanglement in large particle ensembles. Geometrically, this set of conditions defines a convex set of points in the space of first and second moments of the collective $N$particle $su(d)$ operators. We prove that, in the limit $N\gg 1$, such set is filled by pseudoseparable states, while any state corresponding to a point outside of this set is necessarily entangled. We also study states that are detected by these inequalities: We show that states with a bosonic symmetry are detected if and only if the twobody reduced state violates the positive partial transpose (PPT) criterion. On the other hand, highly mixed states states close to the $su(d)$ singlet are detected which have a separable twobody reduced state and are also PPT with respect to all possible bipartitions. We also provide numerical examples of thermal equilibrium states that are detected by our set of inequalities, comparing the spinsqueezing inequalities with the $su(3)$squeezing inequalities.
 [21] arXiv:2406.13343 [pdf, other]

Title: Quantum simulation for strongly interacting fermions with neutral atoms array: towards the simulation of materials of interestComments: Phd manuscriptSubjects: Quantum Physics (quantph)
Quantum simulation holds the promise of improving the atomic simulations used at EDF to anticipate the ageing of materials of interest. One simulator in particular seems well suited to modeling interacting electrons: the Rydberg atoms quantum processor. The first task of this thesis is to design a variational algorithm that can be implemented on a Rydberg atom simulator for chemistry. This algorithm is specially designed for this platform and optimized by recent theoretical tools. We compare our numerical results, obtained with an emulation of a real experiment, with other approaches and show that our method is more efficient. Finally, we show that by limiting the number of measurements to make the experiment feasible on a real architecture, we can reach the fundamental energy of H2, LiH and BeH2 molecules with 5% error.For a second algorithm, we used the "slave" spin method to implement the physics of the FermiHubbard 2D model on a Rydberg atom simulator. The idea is to decouple the degrees of freedom of charges and "slave" spins using a mean field to obtain two selfconsistent Hamiltonians: a classically solvable one and an Ising Hamiltonian that can be reproduced on a real machine. We show numerically that we can recover a Mott transition from the initial model with this method even when emulating the noise of a real experiment, and we show that we can also recover the dynamics of nonequilibrium electrons in this same paradigm with good results. Both algorithms can possibly be improved theoretically until they reach materials of interest, but they can also be implemented on today's existing architectures, to achieve a potential quantum advantage
 [22] arXiv:2406.13349 [pdf, html, other]

Title: Quantumness Speeds up Quantum Thermodynamics ProcessesComments: 18 pagesJournalref: iScience, Volume 27, Issue 5, 109722(2024)Subjects: Quantum Physics (quantph)
Quantum thermodynamic process involves manipulating and controlling quantum states to extract energy or perform computational tasks with high efficiency. There is still no efficientgeneral method to theoretically quantify the effect of the quantumness of coherence and entanglement in work extraction. In this work, we propose a thermodynamics speed to quantify theextracting work. We show that the coherence of quantum systems can speed up work extractingwith respect to some cyclic evolution beyond all incoherent states. We further show the genuine entanglement of quantum systems may speed up work extracting beyond any biseparablestates. This provides a new thermodynamic method to witness entangled systems without statetomography.
 [23] arXiv:2406.13390 [pdf, html, other]

Title: Stabilizing the Kerr arbitrary cat states and holonomic universal controlComments: 17 pages, 12 figuresSubjects: Quantum Physics (quantph)
The interferencefree double potential wells realized by the twophoton driving Kerr nonlinear resonator (KNR) can stabilize cat states and protect them from decoherence through a large energy gap. In this work, we use a parametrically driving KNR to propose a novel engineering Hamiltonian that can stabilize arbitrary cat states and independently manipulate the superposed coherent states to move arbitrarily in phase space. This greater degree of control allows us to make the two potential wells collide and merge, generating a collision state with many novel properties. Furthermore, the potential wells carrying quantum states move adiabatically in phase space produce quantum holonomy. We explore the quantum holonomy of collision states for the first time and propose a holonomyfree preparation method for arbitrary cat states. Additionally, we develop a universal holonomic quantum computing protocol utilizing the quantum holonomy of coherent and collision states, including singlequbit rotation gates and multiqubit control gates. Finally, we propose an experimentally feasible physical realization in superconducting circuits to achieve the Hamiltonian described above. Our proposal provides a platform with greater control degrees of freedom, enabling more operations on bosonic modes and the exploration of intriguing physics.
 [24] arXiv:2406.13403 [pdf, html, other]

Title: Joint qubit observables induced by indirect measurements in cavity QEDComments: 11 pages, 6 figures. Working paper. Comments are very welcome!Subjects: Quantum Physics (quantph)
A fundamental feature of quantum mechanics is that there are observables which can be measured jointly only when some noise is added to them. Their sharp versions are said to be incompatible. In this work we investigate timecontinuous joint qubit observables induced by a indirect timecontinuous measurements. In particular we study a paradigmatic situation where a qubit is interacting with a mode of light in a cavity and the light escaping the cavity is continuously monitored. We find that the properties of the qubit observables can be tuned by changing the type of the monitoring scheme or by tuning the initial state of the cavity. We observe that homodyning two orthogonal quadratures produces an optimal pair of biased jointly measurable qubit observables.
 [25] arXiv:2406.13405 [pdf, html, other]

Title: Gate Teleportation in Noisy Quantum Networks with the SquidASM SimulatorComments: 10 pages, 20 figuresSubjects: Quantum Physics (quantph); Emerging Technologies (cs.ET); Networking and Internet Architecture (cs.NI)
We implement the gate teleportation algorithm for teleporting arbitrary twoqubit Clifford gates and the Toffoli gate within the context of multinode quantum networks, utilizing the SquidASM quantum network simulator. We show how a gate teleportation scheme can be used to implement gate cutting, which is an important approach to realize large circuits in distributed quantum computing environments. The correction operations in teleportation are automatically constructed for arbitrary twoqubit Clifford gates. We present simulation results for CNOT, DCNOT, CZ, SWAP, and Toffoli gates. For the Toffoli gate, we apply a similar gate teleportation protocol with the difference that the correction operation becomes more complex since the gate is nonClifford. We perform the simulations under varying conditions of quantum channel and device noise levels. The simulations provide valuable insights into the robustness and efficacy of the implemented algorithms, and they assist in identifying the critical components within quantum networks where noise primarily affects the execution of applications.
 [26] arXiv:2406.13406 [pdf, html, other]

Title: Photon number distribution of squeezed light from a silicon nitride microresonator measured without photon number resolving detectorsSubjects: Quantum Physics (quantph)
The measurement of the photon number distribution (PND) allows one to extract metrics of nonclassicality of fundamental and technological relevance, but in principle it requires the use of detectors with photon number resolving (PNR) this http URL this work we reconstruct the PND of twomode pulsed squeezed light generated from a silicon nitride microresonator using threshold detectors and variable optical attenuations. The PNDs are characterized up to 1.2 photons/pulse, through which we extracted an onchip squeezing level of 6.2(2) dB and a noise reduction factor of 3.8(2) dB. The PNDs are successfully reconstructed up to an Hilbert space dimension of 6x6. The analysis performed on the photonnumber basis allows us to characterize the influence of a spurious thermal background field that spoils the photon number correlations. We evaluate the impact of self and cross phase modulation on the generation efficiency in case of a pulsed pump, and validate the results through numerical simulations of the master equation of the system.
 [27] arXiv:2406.13412 [pdf, html, other]

Title: Tensor Decompositions and Adiabatic Quantum Computing for Discovering Practical Matrix Multiplication AlgorithmsComments: 12 pages, 6 figuresSubjects: Quantum Physics (quantph); Data Structures and Algorithms (cs.DS)
Quantum computing and modern tensorbased computing have a strong connection, which is especially demonstrated by simulating quantum computations with tensor networks. The other direction is less studied: quantum computing is not often applied to tensorbased problems. Considering tensor decompositions, we focus on discovering practical matrix multiplication algorithms and develop two algorithms to compute decompositions on quantum computers. The algorithms are expressed as higherorder unconstrained binary optimization (HUBO) problems, which are translated into quadratic unconstrained binary optimization (QUBO) problems. Our first algorithm is decompositional to keep the optimization problem feasible for the current quantum devices. Starting from a suitable initial point, the algorithm discovers tensor decomposition corresponding to the famous Strassen matrix multiplication algorithm, utilizing the current quantum annealers. Since the decompositional algorithm does not guarantee minimal length for found tensor decompositions, we develop a holistic algorithm that can find fixedlength decompositions. Theoretically, by fixing a shorter length than the length for the bestknown decomposition, we can ensure that the solution to the holistic optimization problem would yield faster matrix multiplication algorithms.
 [28] arXiv:2406.13430 [pdf, html, other]

Title: Distinguishing a maximally entangled basis using LOCC and shared entanglementComments: 15 pagesSubjects: Quantum Physics (quantph)
We consider the problem of distinguishing between the elements of a bipartite maximally entangled orthonormal basis using LOCC (local operations and classical communication) and a partially entangled state acting as a resource. We derive an exact formula for the optimum success probability and find that it corresponds to the fully entangled fraction of the resource state. The derivation consists of two steps: First, we consider a relaxation of the problem by replacing LOCC with positivepartialtranspose (PPT) measurements and establish an upper bound on the success probability as the solution of a semidefinite program, and then show that this upper bound is achieved by a teleportationbased LOCC protocol. This further implies that separable and PPT measurements provide no advantage over LOCC for this task.
 [29] arXiv:2406.13452 [pdf, html, other]

Title: Quantum Networks: from Multipartite Entanglement to Hypergraph ImmersionComments: 8 pages, 3 figures, 1 tableSubjects: Quantum Physics (quantph); Discrete Mathematics (cs.DM); Social and Information Networks (cs.SI); Computational Physics (physics.compph); Physics and Society (physics.socph)
Multipartite entanglement, a higherorder interaction unique to quantum information, offers various advantages over bipartite entanglement in quantum network (QN) applications. Establishing multipartite entanglement across remote parties in QN requires entanglement routing, which irreversibly transforms the QN topology at the cost of existing entanglement links. Here, we address the question of whether a QN can be topologically transformed into another via entanglement routing. Our key result is an exact mapping from multipartite entanglement routing to NashWilliams's graph immersion problem, extended to hypergraphs. This generalized hypergraph immersion problem introduces a partial order between QN topologies, permitting certain topological transformations while precluding others, offering discerning insights into the design and manipulation of higherorder network topologies in QNs.
 [30] arXiv:2406.13481 [pdf, html, other]

Title: Strong Noninertial Radiative Shifts in Atomic Spectra at Low AccelerationsComments: 8+7 pages, 4 figuresSubjects: Quantum Physics (quantph); General Relativity and Quantum Cosmology (grqc)
Despite numerous proposals investigating various properties of accelerated detectors in different settings, detecting the Unruh effect remains challenging due to the typically weak signal at achievable accelerations. For an atom with frequency gap $\omega_0$, accelerated in free space, significant accelerationinduced modification of properties like transition rates and radiative energy shifts requires accelerations of the order of $\omega_0 c$. In this paper, we make the case for a suitably modified density of field states to be complemented by a judicious selection of the system property to be monitored. We study the radiative energylevel shift in inertial and uniformly accelerated atoms coupled to a massless quantum scalar field inside a cylindrical cavity. Uniformly accelerated atoms experience thermal correlations in the inertial vacuum, and the radiative shifts are expected to respond accordingly. We show that the noninertial contribution to the energy shift can be isolated and significantly enhanced relative to the inertial contribution by suitably modifying the density of field modes inside a cylindrical cavity. Moreover, we demonstrate that monitoring the radiative energy shift, as compared to transition rates, allows us to reap a stronger purelynoninertial signal. We find that a purelynoninertial radiative shift as large as 50 times the inertial energy shift can be obtained at small, experimentally achievable accelerations ($ a \sim 10^{9} \omega_{0} c$) if the cavity's radius $R$ is specified with a relative precision of $\delta R/R_{0} \sim 10^{7}$. Given that radiative shifts for inertial atoms have already been measured with high accuracy, we argue that the radiative energylevel shift is a promising observable for detecting Unruh thermality with current technology.
 [31] arXiv:2406.13491 [pdf, html, other]

Title: Bipartite Bound EntanglementComments: Review Paper, 60 pages, 9 figuresSubjects: Quantum Physics (quantph)
Bound entanglement is a special form of quantum entanglement that cannot be used for distillation, i.e., the local transformation of copies of arbitrarily entangled states into a smaller number of approximately maximally entangled states. Implying an inherent irreversibility of quantum resources, this phenomenon highlights the gaps in our current theory of entanglement. This review provides a comprehensive exploration of the key findings on bipartite bound entanglement. We focus on systems of finite dimensions, an area of high relevance for many quantum information processing tasks. We elucidate the properties of bound entanglement and its interconnections with various facets of quantum information theory and quantum information processing. The article illuminates areas where our understanding of bound entangled states, particularly their detection and characterization, is yet to be fully developed. By highlighting the need for further research into this phenomenon and underscoring relevant open questions, this article invites researchers to unravel its relevance for our understanding of entanglement in Nature and how this resource can most effectively be used for applications in quantum technology.
 [32] arXiv:2406.13492 [pdf, html, other]

Title: Multipartite multiplexing strategies for quantum routersSubjects: Quantum Physics (quantph)
This work explores the important role of quantum routers in communication networks and investigates the increase in efficiency using memories and multiplexing strategies. Motivated by the bipartite setup introduced by Abruzzo et al. (2013) for finiterange multiplexing in quantum repeaters, we extend the study to an Npartite network with a router as a central station. We present a general protocol for N parties after defining the underlying matching problem and we calculate the router rate for different N. We analyze the improvement due to multiplexing, and analyze the secret key rate with explicit results for the tripartite network. Investigating strategic qubit selection for the GHZ measurements, we show that using cutoffs to remove qubits after a certain number of rounds and consistently combining qubits with the lowest number of storage rounds leads to an optimal secret key rate.
 [33] arXiv:2406.13494 [pdf, html, other]

Title: Quantum steering under constrained freewillComments: 10 pages, 5 figuresSubjects: Quantum Physics (quantph)
Quantum steering is a kind of bipartite quantum correlations where one party's measurement remotely alters the state of another party. In an adversarial scenario, there could be a hidden variable introducing a bias in the choice of measurement settings of the parties. However, observers without access to the hidden variable are unaware of this bias. The main focus of this work is to analyze quantum steering without assuming that the parties freely choose their measurement settings. For this, we introduce the measurementdependent (MD)steering scenario where the measurement settings chosen by the parties are biased by an adversary. In such a scenario, we present a class of inequalities to test for MDsteerable correlations. Further, we discuss the implications of violating such inequalities in certifying randomness from quantum extremal behaviors. We also assume that an adversary might prepare an assemblage as a mixture of MDsteerable and MDunsteerable assemblages and provide a bound on the measurement dependence for the observed correlation to remain MDsteerable.
 [34] arXiv:2406.13512 [pdf, html, other]

Title: Managing Temperature in Open Quantum Systems Strongly Coupled with Structured EnvironmentsComments: 24 pages, 14 figures and supplemental materialSubjects: Quantum Physics (quantph); Chemical Physics (physics.chemph)
In nonperturbative nonMarkovian open quantum systems, reaching either low temperatures with the hierarchical equations of motion (HEOM) or high temperatures with the Thermalized Time Evolving Density Operator with Orthogonal Polynomials (TTEDOPA) formalism in Hilbert space remains challenging. We compare different manners of modeling the environment. Sampling the Fourier transform of the bath correlation function, also called temperature dependent spectral density, proves to be very effective. TTEDOPA (Tamascelli et al. Phys. Rev. Lett. 123, 090402 (2019)) uses a linear chain of oscillators with positive and negative frequencies while HEOM is based on the complex poles of an optimized rational decomposition of the temperature dependent spectral density (Xu et al. Phys. Rev. Lett. 129, 230601 (2022)). Resorting to the poles of the temperature independent spectral density and of the Bose function separately is an alternative when the problem due to the huge number of the Bose poles at low temperature is circumvented. Two examples illustrate the effectiveness of the HEOM and TTEDOPA approaches: a benchmark pure dephasing case and a twobath model simulating dynamics of excited electronic states coupled through a conical intersection. We show the efficiency of TTEDOPA to simulate dynamics at a finite temperature by using either continuous spectral densities or only all the intramolecular oscillators of a linear vibronic model calibrated from ab initio data of a phenylene ethynylene dimer.
 [35] arXiv:2406.13517 [pdf, html, other]

Title: Quantifying nonHermiticity using single and manyparticle quantum propertiesComments: 13 pages, 6 figuresSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas); Strongly Correlated Electrons (condmat.strel)
The nonHermitian paradigm of quantum systems displays salient features drastically different from Hermitian counterparts. In this work, we focus on one such aspect, the difference of evolving quantum ensembles under $H_{\mathrm{nh}}$ (right ensemble) versus its Hermitian conjugate, $H_{\mathrm{nh}}^{\dagger}$ (left ensemble). We propose a formalism that quantifies the (dis)similarity of these right and left ensembles, for single as well as manyparticle quantum properties. Such a comparison gives us a scope to measure the extent to which nonHermiticity gets translated from the Hamiltonian into physically observable properties. We test the formalism in two cases: First, we construct a nonHermitian Hamiltonian using a set of imperfect Bell states, showing that the nonHermiticity of the Hamiltonian does not automatically comply with the nonHermiticity at the level of observables. Second, we study the interacting HatanoNelson model with asymmetric hopping as a paradigmatic quantum manybody Hamiltonian. Interestingly, we identify situations where the measures of nonHermiticity computed for the Hamiltonian, for single, and for manyparticle quantum properties behave distinctly from each other. Thus, different notions of nonHermiticity can become useful in different physical scenarios. Furthermore, we demonstrate that the measures can mark the model's ParityTime (PT) symmetrybreaking transition. Our findings can be instrumental in unveiling new exotic quantum phases of nonHermitian quantum manybody systems as well as in preparing resourceful states for quantum technologies.
 [36] arXiv:2406.13572 [pdf, html, other]

Title: Entanglement source and quantum memory analysis for zero addedloss multiplexingComments: 26 pages, 15 figure, 1 tableSubjects: Quantum Physics (quantph)
Highrate, highfidelity entanglement distribution is essential to the creation of a quantum internet, but recent achievements in fiber and satellitebased entanglement distribution fall far short of what is needed. Chen et al. [Phys. Rev. Appl. 19, 054209 (2023)] proposed a means for dramatically increasing entanglementdistribution rates via zero addedloss multiplexing (ZALM). ZALM's quantum transmitter employs a pair of Sagnacconfigured spontaneous parametric downconverters (SPDCs), channelization via dense wavelengthdivision multiplexing (DWDM) filtering, and partial Bellstate measurements (BSMs) to realize a neardeterministic, heralded source of frequencymultiplexed polarizationentangled biphotons. Each biphoton is transmitted to Alice and Bob with a classical message identifying its frequency channel and the heralded entangled state. Their quantum receivers use DWDM filtering and mode conversion to interface their received biphotons to intracavity colorcenter quantum memories. This paper delves deeply into ZALM's SPDCs, partialBSMs, and loading of Alice and Bob's quantum memories. It derives the density operators for the SPDC sources and the quantum memories, allowing heralding probability, heralding efficiency, and fidelity to be evaluated for both the polarizationentangled biphotons and the loaded quantum memories, thus enabling exploration of the parameter space for optimizing ZALM performance. Even without optimization analysis, the paper already demonstrates two critical features of the ZALM architecture: the necessity of achieving a nearseparable channelized biphoton wave function to ensure the biphoton sent to Alice and Bob is of high purity; and the premium placed on Alice and Bob's temporalmode converters' enabling narrowband pushpull memory loading to ensure the arriving biphoton's state is faithfully transferred to the intracavity color centers.
 [37] arXiv:2406.13577 [pdf, html, other]

Title: Genuine Multipartite Entanglement induced by a Thermal Acoustic ReservoirComments: 25 pages, 9 figuresSubjects: Quantum Physics (quantph)
Genuine multipartite entanglement (GME) is not only fundamental interesting for the study of quantumtoclassical transition, but also is essential for realizing universal quantum computing and quantum networks. Here we investigate the multipartite entanglement (ME) dynamics in a linear chain of N LC resonators interacting optomechanically with a common thermal acoustic reservoir. By presenting the exact analytical solutions of system evolution, we predict the periodic generation of nonGaussian ME, including the discrete and continuous variables entanglement. Interestingly, the GME is obtained even though the system is in a heat bath. The mechanism relies on the special acoustic environment featuring frequency comb structure. More importantly, our proposed model also allows the periodic generation of entangled multipartite cat states (MCSs), i.e., a typical GHZ state, with high fidelity. This work fundamentally broadens the fields of ME, and have wide applications in implementing thermalnoiseresistant quantum information processing and manybody quantum simulation.
 [38] arXiv:2406.13611 [pdf, html, other]

Title: Solving kSAT problems with generalized quantum measurementComments: 23 + 8 pages, 15 figuresSubjects: Quantum Physics (quantph)
We generalize the projectionbased quantum measurementdriven $k$SAT algorithm of Benjamin, Zhao, and Fitzsimons (BZF, arXiv:1711.02687) to arbitrary strength quantum measurements, including the limit of continuous monitoring. In doing so, we clarify that this algorithm is a particular case of the measurementdriven quantum control strategy elsewhere referred to as "Zeno dragging". We argue that the algorithm is most efficient with finite time and measurement resources in the continuum limit, where measurements have an infinitesimal strength and duration. Moreover, for solvable $k$SAT problems, the dynamics generated by the algorithm converge deterministically towards target dynamics in the longtime (Zeno) limit, implying that the algorithm can successfully operate autonomously via Lindblad dissipation, without detection. We subsequently study both the conditional and unconditional dynamics of the algorithm implemented via generalized measurements, quantifying the advantages of detection for heralding errors. These strategies are investigated first in a computationallytrivial $2$qubit $2$SAT problem to build intuition, and then we consider the scaling of the algorithm on $3$SAT problems encoded with $4  10$ qubits. The average number of shots needed to obtain a solution scales with qubit number as $\lambda^n$. For vanishing dragging time (with final readout only), we find $\lambda = 2$ (corresponding to a bruteforce search over possible solutions). However, the deterministic (autonomous) property of the algorithm in the adiabatic (Zeno) limit implies that we can drive $\lambda$ arbitrarily close to $1$, at the cost of a growing prefactor. We numerically investigate the tradeoffs in these scalings with respect to algorithmic runtime and assess their implications for using this analog measurementdriven approach to quantum computing in practice.
 [39] arXiv:2406.13616 [pdf, html, other]

Title: Entangled Matterwaves for Quantum Enhanced SensingJohn Drew Wilson, Jarrod T. Reilly, Haoqing Zhang, Chengyi Luo, Anjun Chu, James K. Thompson, Ana Maria Rey, Murray J. HollandSubjects: Quantum Physics (quantph); Atomic and Molecular Clusters (physics.atmclus)
The ability to create and harness entanglement is crucial to the fields of quantum sensing andsimulation, and ultracold atomcavity systems offer pristine platforms for this undertaking. Recently, an experiment demonstrated an effective momentumexchange interaction between atoms in a common cavity mode. Here, we derive this interaction from a general atomcavity model, and discuss the role of the cavity frequency shift in response to atomic motion. We show the cavity response leads to many different squeezing interactions between the atomic momentum states. Furthermore, when the atoms form a density grating, the collective motion leads to oneaxis twisting, a manybody energy gap, and metrologically useful entanglement even in the presence of noise. This system offers a highly tunable, manybody quantum sensor and simulator.
 [40] arXiv:2406.13678 [pdf, html, other]

Title: Simulating open quantum systems with giant atomsComments: 15+4 pages, 8+2 figures, source codes will be available at this https URLSubjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel)
Open quantum manybody systems are of both fundamental and applicational interest. However, it remains an open challenge to simulate and solve such systems, both with stateoftheart classical methods and with quantumsimulation protocols. To overcome this challenge, we introduce a simulator for open quantum manybody systems based on giant atoms, i.e., atoms (possibly artificial), that couple to a waveguide at multiple points, which can be wavelengths apart. We first show that a simulator consisting of two giant atoms can simulate the dynamics of two coupled qubits, where one qubit is subject to different drive amplitudes and dissipation rates. This simulation enables characterizing the quantum Zeno crossover in this model. We further show that by equipping the simulator with postselection, it becomes possible to simulate the effective nonHermitian Hamiltonian dynamics of the system and thereby characterize the transition from oscillatory to nonoscillatory dynamics due to varying dissipation rates. We demonstrate and analyze the robustness of these simulation results against noise affecting the giant atoms. Finally, we discuss and show how giantatombased simulators can be scaled up for digitalanalog simulation of large open quantum manybody systems, e.g., generic dissipative spin models.
 [41] arXiv:2406.13760 [pdf, html, other]

Title: Hacking coherentoneway quantum key distribution with presentday technologyJournalref: Quantum Sci. Technol. 9, 035044 (2024)Subjects: Quantum Physics (quantph)
Recent results have shown that the secretkey rate of coherentoneway (COW) quantum key distribution (QKD) scales quadratically with the system's transmittance, thus rendering this protocol unsuitable for longdistance transmission. This was proven by using a socalled zeroerror attack, which relies on an unambiguous state discrimination (USD) measurement. This type of attack allows the eavesdropper to learn the whole secret key without introducing any error. Here, we investigate the feasibility and effectiveness of zeroerror attacks against COW QKD with presentday technology. For this, we introduce two practical USD receivers that can be realized with linear passive optical elements, phasespace displacement operations and threshold singlephoton detectors. The first receiver is optimal with respect to its success probability, while the second one can impose stronger restrictions on the protocol's performance with faulty eavesdropping equipment. Our findings suggest that zeroerror attacks could break the security of COW QKD even assuming realistic experimental conditions.
 [42] arXiv:2406.13775 [pdf, html, other]

Title: Finite (quantum) effect algebrasSubjects: Quantum Physics (quantph)
We investigate finite effect algebras and their classification. We show that an effect algebra with $n$ elements has at least $n2$ and at most $(n1)(n2)/2$ nontrivial defined sums. We characterize finite effect algebras with these minimal and maximal number of defined sums. The latter effect algebras are scale effect algebras (i.e., subalgebras of [0,1]), and only those. We prove that there is exactly one scale effect algebra with $n$ elements for every integer $n \geq 2$. We show that a finite effect algebra is quantum effect algebra (i.e. a subeffect algebra of the standard quantum effect algebra) if and only if it has a finite set of orderdetermining states. Among effect algebras with 26 elements, we identify all quantum effect algebras.
 [43] arXiv:2406.13785 [pdf, html, other]

Title: Efficient Implementation of a Quantum Search Algorithm for Arbitrary NComments: 6 pagesSubjects: Quantum Physics (quantph)
This paper presents an enhancement to Grover's search algorithm for instances where the number of items (or the size of the search problem) $N$ is not a power of 2. By employing an efficient algorithm for the preparation of uniform quantum superposition states over a subset of the computational basis states, we demonstrate that a considerable reduction in the number of oracle calls (and Grover's iterations) can be achieved in many cases. For special cases (i.e., when $N$ is of the form such that it is slightly greater than an integer power of 2), the reduction in the number of oracle calls (and Grover's iterations) asymptotically approaches 29.33\%. This improvement is significant compared to the traditional Grover's algorithm, which handles such cases by rounding $N$ up to the nearest power of 2. The key to this improvement is our algorithm for the preparation of uniform quantum superposition states over a subset of the computational basis states, which requires gate complexity and circuit depth of only $ O (\log_2 (N)) $, without using any ancilla qubits.
 [44] arXiv:2406.13812 [pdf, html, other]

Title: Singleshot quantum machine learningComments: 12+6 pagesSubjects: Quantum Physics (quantph)
Quantum machine learning aims to improve learning methods through the use of quantum computers. If it is to ever realize its potential, many obstacles need to be overcome. A particularly pressing one arises at the prediction stage because the outputs of quantum learning models are inherently random. This creates an often considerable overhead, as many executions of a quantum learning model have to be aggregated to obtain an actual prediction. In this work, we analyze when quantum learning models can evade this issue and produce predictions in a neardeterministic way  paving the way to singleshot quantum machine learning. We give a rigorous definition of singleshotness in quantum classifiers and show that the degree to which a quantum learning model is neardeterministic is constrained by the distinguishability of the embedded quantum states used in the model. Opening the black box of the embedding, we show that if the embedding is realized by quantum circuits, a certain depth is necessary for singleshotness to be even possible. We conclude by showing that quantum learning models cannot be singleshot in a generic way and trainable at the same time.
 [45] arXiv:2406.13823 [pdf, other]

Title: Inevitable Negativity: Additivity Commands Negative Quantum Channel EntropyComments: 16 pages (main text) + 21 pages (appendix), 6 figures, comments are welcomeSubjects: Quantum Physics (quantph); Mathematical Physics (mathph)
Quantum channels represent a broad spectrum of operations crucial to quantum information theory, encompassing everything from the transmission of quantum information to the manipulation of various resources. In the domain of states, the concept of majorization serves as a fundamental tool for comparing the uncertainty inherent in both classical and quantum systems. This paper establishes a rigorous framework for assessing the uncertainty in both classical and quantum channels. By employing a specific class of superchannels, we introduce and elucidate three distinct approaches to channel majorization: constructive, axiomatic, and operational. Intriguingly, these methodologies converge to a consistent ordering. This convergence not only provides a robust basis for defining entropy functions for channels but also clarifies the interpretation of entropy in this broader context. Most notably, our findings reveal that any viable entropy function for quantum channels must assume negative values, thereby challenging traditional notions of entropy.
 [46] arXiv:2406.13830 [pdf, html, other]

Title: Quantum spin systems: toroidal classification and geometric dualityVahid AzimiMousolou, Anders Bergman, Anna Delin, Olle Eriksson, Manuel Pereiro, Danny Thonig, Erik SjöqvistComments: 6 pages, 2 figuresSubjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall)
Toroidal classification and geometric duality in quantum spin systems is presented. Through our classification and duality, we reveal that various bipartite quantum features in magnonsystems can manifest equivalently in both bipartite ferromagnetic and antiferromagnetic materials, based upon the availability of relevant Hamiltonian parameters. Additionally, the results highlight the antiferromagnetic regime as an ultrafast dual counterpart to the ferromagnetic regime, both exhibiting identical capabilities for quantum spintronics and technological applications. Concrete illustrations are provided, demonstrating how splitting and squeezing types of twomode magnon quantum correlations can be realized across ferro and antiferromagnetic regimes.
 [47] arXiv:2406.13879 [pdf, html, other]

Title: A Catalyst Framework for the Quantum Linear System Problem via the Proximal Point AlgorithmSubjects: Quantum Physics (quantph); Data Structures and Algorithms (cs.DS); Machine Learning (cs.LG); Optimization and Control (math.OC)
Solving systems of linear equations is a fundamental problem, but it can be computationally intensive for classical algorithms in high dimensions. Existing quantum algorithms can achieve exponential speedups for the quantum linear system problem (QLSP) in terms of the problem dimension, but even such a theoretical advantage is bottlenecked by the condition number of the coefficient matrix. In this work, we propose a new quantum algorithm for QLSP inspired by the classical proximal point algorithm (PPA). Our proposed method can be viewed as a metaalgorithm that allows inverting a modified matrix via an existing \texttt{QLSP\_solver}, thereby directly approximating the solution vector instead of approximating the inverse of the coefficient matrix. By carefully choosing the step size $\eta$, the proposed algorithm can effectively precondition the linear system to mitigate the dependence on condition numbers that hindered the applicability of previous approaches.
 [48] arXiv:2406.13901 [pdf, html, other]

Title: Efficient ChromaticNumberBased MultiQubit Decoherence and Crosstalk SuppressionComments: 6 pages, 2 figuresSubjects: Quantum Physics (quantph)
The performance of quantum computers is hindered by decoherence and crosstalk, which cause errors and limit the ability to perform long computations. Dynamical decoupling is a technique that alleviates these issues by applying carefully timed pulses to individual qubits, effectively suppressing unwanted interactions. However, as quantum devices grow in size, it becomes increasingly important to minimize the time required to implement dynamical decoupling across the entire system. Here, we present "ChromaticHadamard Dynamical Decoupling" (CHaDD), an approach that efficiently schedules dynamical decoupling pulses for quantum devices with arbitrary qubit connectivity. By leveraging Hadamard matrices, CHaDD achieves a circuit depth that scales quadratically with the chromatic number of the connectivity graph for general twoqubit interactions, assuming instantaneous pulses. For the common case of ZZ crosstalk, which is prevalent in superconducting qubit devices, the scaling improves to linear. This represents an exponential improvement over all previous multiqubit decoupling schemes for devices with connectivity graphs whose chromatic number grows at most polylogarithmically with the number of qubits. For graphs with a constant chromatic number, CHaDD's scaling is independent of the number of qubits. Our results suggest that CHaDD can become a useful tool for enhancing the performance and scalability of quantum computers by efficiently suppressing decoherence and crosstalk across large qubit arrays.
 [49] arXiv:2406.13916 [pdf, html, other]

Title: A reconfigurable entanglement distribution network suitable for connecting multiple ground nodes with a satelliteSubjects: Quantum Physics (quantph)
Bridging the long distances between different metropolitanscale quantum networks is currently best achieved using satellites, which can cover thousands of kilometres. The development of efficient approaches to establish connectivity between ground nodes and a satellite is therefore an essential next step. We propose a network with dualfunctionality: during a brief satellite pass, the ground network is configured as a multipointtopoint topology where all ground nodes establish entanglement with a satellite receiver. During times when this satellite is not available, the satellite uplink is rerouted via a single optical switch to the ground nodes, and the network is configured as a pairwise ground network. We numerically simulate a pulsed hyperentangled photon source and study the performance of the proposed network configurations for quantum key distribution. We find favourable resource overheads in the case that the satellite receiver exploits timemultiplexing whereas the ground nodes utilize frequencymultiplexing. Our results show high and scalable key rates can be achieved in both configurations. The scalability, simple reconfigurability, and easy integration with fibre networks make this architecture a promising candidate for quantum communication of many ground nodes and a satellite thus paving the way towards interconnection of ground nodes at a global scale.
 [50] arXiv:2406.13921 [pdf, html, other]

Title: Quantum Enhanced Sensitivity through ManyBody Bloch OscillationsSubjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel)
We investigate the sensing capacity of nonequilibrium dynamics in quantum systems exhibiting Bloch oscillations. By focusing on resource efficiency of the probe, quantified by quantum Fisher information, we find different scaling behaviors in two different phases, namely localized and extended. Our results provide a quantitative ansatz for quantum Fisher information in terms of time, probe size, and the number of excitations. In the longtime regime, the quantum Fisher information is a quadratic function of time, touching the Heisenberg limit. The system size scaling drastically depends on the phase changing from superHeisenberg scaling in the extended phase to sizeindependent behavior in the localized phase. Furthermore, increasing the number of excitations always enhances the precision of the probe, although, in the interacting systems the enhancement becomes less eminent than the noninteracting probes, which is due to induced localization by interaction between excitations.
 [51] arXiv:2406.13937 [pdf, html, other]

Title: DistiMator: an entanglement distillationbased state estimatorJoshua Carlo A. Casapao, Ananda G. Maity, Naphan Benchasattabuse, Michal Hajdušek, Rodney Van Meter, David ElkoussComments: 14+5 pages, 5 figures, comments are welcomeSubjects: Quantum Physics (quantph)
Minimizing both experimental effort and consumption of valuable quantum resources in state estimation is vital in practical quantum information processing. Here, we explore characterizing states as an additional benefit of the entanglement distillation protocols. We show that the Belldiagonal parameters of any undistilled state can be efficiently estimated solely from the measurement statistics of probabilistic distillation protocols. We further introduce the state estimator `DistiMator' designed specifically for a realistic experimental setting, and exhibit its robustness through numerical simulations. Our results demonstrate that a separate estimation protocol can be circumvented whenever distillation is an indispensable communicationbased task.
 [52] arXiv:2406.13957 [pdf, html, other]

Title: Stabilization of Kerrcat qubits with quantum circuit refrigeratorSubjects: Quantum Physics (quantph)
A periodicallydriven superconducting nonlinear resonator can implement a Kerrcat qubit, which provides a promising route to a quantum computer with a long lifetime. However, the system is vulnerable to pure dephasing, which causes unwanted excitations outside the qubit subspace. Therefore, we require a refrigeration technology which confines the system in the qubit subspace. We theoretically study onchip refrigeration for Kerrcat qubits based on photonassisted electron tunneling at tunneling junctions, called quantum circuit refrigerator (QCR). Rates of QCRinduced deexcitations of the system can be changed by more than four orders of magnitude by tuning a bias voltage across the tunneling junctions. Unwanted QCRinduced bit flips are greatly suppressed due to quantum interference in the tunneling process, and thus the long lifetime is preserved. The QCR can serve as a tunable dissipation source which stabilizes Kerrcat qubits.
 [53] arXiv:2406.13967 [pdf, html, other]

Title: HardwareEfficient Randomized CompilingNeelay Fruitwala, Akel Hashim, Abhi D. Rajagopala, Yilun Xu, Jordan Hines, Ravi K. Naik, Irfan Siddiqi, Katherine Klymko, Gang Huang, Kasra NowrouziSubjects: Quantum Physics (quantph)
Randomized compiling (RC) is an efficient method for tailoring arbitrary Markovian errors into stochastic Pauli channels. However, the standard procedure for implementing the protocol in software comes with a large experimental overhead  namely, it scales linearly in the number of desired randomizations, each of which must be generated and measured independently. In this work, we introduce a hardwareefficient algorithm for performing RC on a cyclebycycle basis on the lowest level of our FPGAbased control hardware during the execution of a circuit. Importantly, this algorithm performs a different randomization per shot with zero runtime overhead beyond measuring a circuit without RC. We implement our algorithm using the QubiC control hardware, where we demonstrate significant reduction in the overall runtime of circuits implemented with RC, as well as a significantly lower variance in measured observables.
 [54] arXiv:2406.13999 [pdf, html, other]

Title: Individually Addressed Entangling Gates in a TwoDimensional Ion CrystalY.H. Hou, Y.J. Yi, Y.K. Wu, Y.Y. Chen, L. Zhang, Y. Wang, Y.L. Xu, C. Zhang, Q.X. Mei, H.X. Yang, J.Y. Ma, S.A. Guo, J. Ye, B.X. Qi, Z.C. Zhou, P.Y. Hou, L.M. DuanSubjects: Quantum Physics (quantph)
Twodimensional (2D) ion crystals have become a promising way to scale up qubit numbers for ion trap quantum information processing. However, to realize universal quantum computing in this system, individually addressed highfidelity twoqubit entangling gates still remain challenging due to the inevitable micromotion of ions in a 2D crystal as well as the technical difficulty in 2D addressing. Here we demonstrate twoqubit entangling gates between any ion pairs in a 2D crystal of four ions. We use symmetrically placed crossed acoustooptic deflectors (AODs) to drive Raman transitions and achieve an addressing crosstalk error below 0.1%. We design and demonstrate a gate sequence by alternatingly addressing two target ions, making it compatible with any singleion addressing techniques without crosstalk from multiple addressing beams. We further examine the gate performance versus the micromotion amplitude of the ions and show that its effect can be compensated by a recalibration of the laser intensity without degrading the gate fidelity. Our work paves the way for ion trap quantum computing with hundreds to thousands of qubits on a 2D ion crystal.
 [55] arXiv:2406.14078 [pdf, html, other]

Title: Single Bell inequality to detect genuine nonlocality in threequbit genuinely entangled statesComments: 9 pages, 1 figureSubjects: Quantum Physics (quantph)
It remains an open question whether every pure multipartite state that is genuinely entangled is also genuinely nonlocal. Recently, a new general construction of Bell inequalities allowing the detection of genuine multipartite nonlocality (GMNL) in quantum states was proposed in [F. J. Curchod, M. L. Almeida, and A. Acin, New J. Phys. 21, 023016 (2019) with the aim of addressing the above problem. Here we show how, in a simple manner, one can improve this construction to deliver tighter Bell inequalities for detection of GMNL. Remarkably, we then prove one of the improved Bell inequalities to be powerful enough to detect GMNL in every threequbit genuinely entangled state. We also generalize some of these inequalities to detect not only GMNL but also nonlocality depth in multipartite states and we present a possible way of generalizing them to the case of more outcomes.
 [56] arXiv:2406.14084 [pdf, other]

Title: Queen: A quick, scalable, and comprehensive quantum circuit simulation for supercomputingSubjects: Quantum Physics (quantph); Performance (cs.PF)
The state vectorbased simulation offers a convenient approach to developing and validating quantum algorithms with noisefree results. However, limited by the absence of cacheaware implementations and unpolished circuit optimizations, the past simulators were severely constrained in performance, leading to stagnation in quantum computing. In this paper, we present an innovative quantum circuit simulation toolkit comprising gate optimization and simulation modules to address these performance challenges. For the performance, scalability, and comprehensive evaluation, we conduct a series of particular circuit benchmarks and strong scaling tests on a DGXA100 workstation and achieve averaging 9 times speedup compared to stateoftheart simulators, including QuEST, IBMAer, and NVIDIAcuQuantum. Moreover, the critical performance metric FLOPS increases by up to a factor of 8fold, and arithmetic intensity experiences a remarkable 96x enhancement. We believe the proposed toolkit paves the way for faster quantum circuit simulations, thereby facilitating the development of novel quantum algorithms.
 [57] arXiv:2406.14109 [pdf, html, other]

Title: Protect MeasurementInduced Phase Transition from NoiseSubjects: Quantum Physics (quantph); Disordered Systems and Neural Networks (condmat.disnn); Statistical Mechanics (condmat.statmech)
Measurementinduced phase transition (MIPT) is a novel nonequilibrium phase transition characterized by entanglement entropy. The scrambling dynamics induced by random unitary gates can protect information from lowrate measurements. However, common decoherence noises, such as dephasing, are detrimental to the volume law phase, posing a significant challenge for observing MIPT in current noisy intermediatescale quantum devices. Here, we demonstrate that incorporating quantumenhanced operations can effectively protect MIPT from environmental noise. The conditional entanglement entropy is associated with a statistical mechanics model wherein noise and quantumenhanced operations act as two competing external random fields. Then we show that an average apparatusenvironment exchange symmetry ensures the conditional entanglement entropy is a valid probe of entanglement. Furthermore, we provide numerical evidence on a (2+1)d quantum circuit under dephasing noise, demonstrating that MIPT can indeed be observed with the aid of quantumenhanced operations. This result not only serves as a concrete example of the power of quantum enhancement in combating noise but also holds experimental relevance, as the protocol is straightforward to implement in practice.
 [58] arXiv:2406.14112 [pdf, html, other]

Title: Skin effect in quantum neural networksComments: Comments are welcomeSubjects: Quantum Physics (quantph)
In the field of dissipative systems, the nonHermitian skin effect has generated significant interest due to its unexpected implications. A system is said to exhibit a skin effect if its properties are largely affected by the boundary conditions. Despite the burgeoning interest, the potential impact of this phenomenon on emerging quantum technologies remains unexplored. In this work, we address this gap by demonstrating that quantum neural networks can exhibit this behavior and that skin effects, beyond their fundamental interest, can also be exploited in computational tasks. Specifically, we show that the performance of a given complex network used as a quantum reservoir computer is dictated solely by the boundary conditions of a dissipative line within its architecture. The closure of one (edge) link is found to drastically change the performance in time series processing proving the possibility to exploit skin effects for machine learning.
 [59] arXiv:2406.14113 [pdf, html, other]

Title: A differentiable quantum phase estimation algorithmSubjects: Quantum Physics (quantph); Computational Physics (physics.compph)
The simulation of electronic properties is a pivotal issue in modern electronic structure theory, driving significant efforts over the past decades to develop protocols for computing energy derivatives. In this work, we address this problem by developing a strategy to integrate the quantum phase estimation algorithm within a fully differentiable framework. This is accomplished by devising a smooth estimator able to tackle arbitrary initial states. We provide analytical expressions to characterize the statistics and algorithmic cost of this estimator. Furthermore, we provide numerical evidence that the estimation accuracy is retained when an arbitrary state is considered and that it exceeds the one of standard majority rule. We explicitly use this procedure to estimate chemically relevant quantities, demonstrating our approach through groundstate and triplet excited state geometry optimization with simulations involving up to 19 qubits. This work paves the way for new quantum algorithms that combine interference methods and quantum differentiable programming.
 [60] arXiv:2406.14127 [pdf, html, other]

Title: VariationalCartan Quantum Dynamics Simulations of Excitation DynamicsSubjects: Quantum Physics (quantph)
Quantum dynamics simulations (QDSs) are one of the most highly anticipated applications of quantum computing. Quantum circuit depth for implementing Hamiltonian simulation algorithms is commonly time dependent so that long time dynamics simulations become impratical on nearterm quantum processors. The Hamiltonian simulation algorithm based on Cartan decomposition (CD) provides an appealing scheme for QDSs with fixeddepth circuits while limited to timeindependent case. In this work, we generalize this CDbased Hamiltonian simulation algorithm for studying timedependent systems by combining it with variational Hamiltonian simulation. The timedependent and timeindependent parts of the Hamiltonian are treated with the variational approach and the CDbased Hamiltonian simulation algorithms, respectively. As such, only fixeddepth quantum circuits are required in this hybrid Hamiltonian simulation algorithm while still maintaining high accuracy. We apply this new algorithm to study the response of spin and molecular systems to $\delta$kick electric fields and obtain accurate spectra for these excitation processes.
 [61] arXiv:2406.14153 [pdf, html, other]

Title: On random classical marginal problems with applications to quantum information theorySubjects: Quantum Physics (quantph); Mathematical Physics (mathph); Probability (math.PR)
In this paper, we study random instances of the classical marginal problem. We encode the problem in a graph, where the vertices have assigned fixed binary probability distributions, and edges have assigned random bivariate distributions having the incident vertex distributions as marginals. We provide estimates on the probability that a joint distribution on the graph exists, having the bivariate edge distributions as marginals. Our study is motivated by Fine's theorem in quantum mechanics. We study in great detail the graphs corresponding to CHSH and BellWigner scenarios providing rations of volumes between the local and nonsignaling polytopes.
 [62] arXiv:2406.14166 [pdf, html, other]

Title: DiscreteModulated ContinuousVariable Quantum Key Distribution in SatellitetoGround CommunicationComments: 12 pages, 6 figuresJournalref: Advanced Quantum Technologies 7, 2400140 (2024)Subjects: Quantum Physics (quantph)
Satellitetoground quantum communication constitutes the cornerstone of the global quantum network, heralding the advent of the future of quantum information. Continuousvariable quantum key distribution is a strong candidate for spaceground quantum communication due to its simplicity, stability, and ease of implementation, especially for the robustness of space background light noise. Recently, the discretemodulated continuousvariable protocol has garnered increased attention, owing to its lower implementation requirements, acceptable security key rate, and pronounced compatibility with extant infrastructures. Here, we derive key rates for discretemodulated continuousvariable quantum key distribution protocols in freespace channel environments across various conditions through numerical simulation, revealing the viability of its application in satellitetoground communication.
 [63] arXiv:2406.14170 [pdf, html, other]

Title: Compact fermionic quantum state preparation with a naturalorbitalizing variational quantum eigensolving schemeSubjects: Quantum Physics (quantph)
Assemblies of strongly interacting fermions, whether in a condensedmatter or a quantum chemistry context, range amongst the most promising candidate systems for which quantum computing platforms could provide an advantage. Nearterm quantum state preparation is typically realized by means of the variational quantum eigensolver (VQE) algorithm. One of the main challenges to a successful implementation of VQE lies in the sensitivity to noise exhibited by deep variational circuits. On the other hand, sufficient depth must be allowed to be able to reach a good approximation to the target state. In this work, we present a refined VQE scheme that consists in topping VQE with stateinformed updates of the elementary fermionic modes (spinorbitals). These updates consist in moving to the naturalorbital basis of the current, converged variational state, a basis we argue eases the task of state preparation. We test the method on the Hubbard model in the presence of experimentally relevant noise levels. For a fixed circuit structure, the method is shown to enhance the capabilities of the circuit to reach a state close to the target state without incurring too much overhead from shot noise. Moreover, coupled with an adaptive VQE scheme that constructs the circuit on the fly, we evidence reduced requirements on the depth of the circuit as the orbitals get updated.
 [64] arXiv:2406.14216 [pdf, html, other]

Title: RepeaterBased Quantum Communication Protocol: Maximizing Teleportation Fidelity with Minimal EntanglementComments: (4.5+11.5, 4 figures)Subjects: Quantum Physics (quantph)
Transmitting unknown quantum states to distant locations is crucial for distributed quantum information protocols. The seminal quantum teleportation scheme achieves this feat while requiring prior maximal entanglement between the sender and receiver. In scenarios with noisy entangled states, optimal teleportation fidelity characterizes the efficacy of transmitting the state, demanding the proper selection of local operations at the sender's and receiver's ends. The complexity escalates further in longrange communication setups, prompting the consideration of a repeaterbased approach, which incorporates arrays of nodes with multiple segments to facilitate the efficient transmission of quantum information. The fidelity of the communication line gets degraded even if a single segment is affected by noise. In such cases, the general wisdom employs the standard entanglement swapping protocol involving maximally entangled states across the noiseless segments and applying maximally entangled basis measurement at the corresponding nodes to achieve optimal fidelity. In this Letter, we propose a more efficient protocol for a certain class of noisy states in any intermediary segment, achieving the same fidelity as the standard protocol while consuming less amount of entanglement. Our approach ensures enhanced teleportation fidelity even when the endtoend state gets noisier, and thus promises efficient utility of quantum resources in repeaterbased distributed quantum protocols.
 [65] arXiv:2406.14225 [pdf, html, other]

Title: Comment on "Covariant quantum field theory of tachyons"Comments: 5 pages, 1 figure; comment to arXiv:2308.00450, which was accepted by PRDSubjects: Quantum Physics (quantph); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
Recently, Paczos et al. (2308.00450) proposed a covariant quantum field theory for free and interacting tachyon fields. We show that the proposed Feynman propagator is not Lorentz invariant, proper asymptotic (in/out) tachyon states do not exist, and the proposed Smatrix describing interactions of tachyons and subluminal matter is illdefined. Since tachyons behave as bosons, interacting tachyons may also selfinteract, e.g., any interaction with ordinary matter generates such terms. As a result, the physical vacuum, instead of being at the origin of the potential, may correspond to the proper minimum of the tachyon potential, or such state does not exist at all. Our analysis indicates that quantum tachyon field does not describe a physical onshell particle with negative mass squared.
 [66] arXiv:2406.14236 [pdf, other]

Title: NACQFL: Noise Aware Clustered Quantum Federated LearningSubjects: Quantum Physics (quantph); Distributed, Parallel, and Cluster Computing (cs.DC)
Recent advancements in quantum computing, alongside successful deployments of quantum communication, hold promises for revolutionizing mobile networks. While Quantum Machine Learning (QML) presents opportunities, it contends with challenges like noise in quantum devices and scalability. Furthermore, the high cost of quantum communication constrains the practical application of QML in realworld scenarios. This paper introduces a noiseaware clustered quantum federated learning system that addresses noise mitigation, limited quantum device capacity, and high quantum communication costs in distributed QML. It employs noise modelling and clustering to select devices with minimal noise and distribute QML tasks efficiently. Using circuit partitioning to deploy smaller models on lownoise devices and aggregating similar devices, the system enhances distributed QML performance and reduces communication costs. Leveraging circuit cutting, QML techniques are more effective for smaller circuit sizes and fidelity. We conduct experimental evaluations to assess the performance of the proposed system. Additionally, we introduce a noisy dataset for QML to demonstrate the impact of noise on proposed accuracy.
 [67] arXiv:2406.14252 [pdf, html, other]

Title: Beyond QUBO and HOBO formulations, solving the Travelling Salesman Problem on a quantum boson samplerComments: 16 pages and 4 figuresSubjects: Quantum Physics (quantph)
The Travelling Salesman Problem (TSP) is an important combinatorial optimisation problem, and is usually solved on a quantum computer using a Quadratic Unconstrained Binary Optimisation (QUBO) formulation or a Higher Order Binary Optimisation(HOBO) formulation. In these formulations, penalty terms are added to the objective function for outputs that don't map to valid routes.
We present a novel formulation which needs fewer binary variables, and where, by design, there are no penalty terms because all outputs from the quantum device are mapped to valid routes. Simulations of a quantum boson sampler were carried out which demonstrate that larger networks can be solved with this penaltyfree formulation than with formulations with penalties. Simulations were successfully translated to hardware by running a nonQUBO formulation with penalties on an early experimental prototype ORCA PT1 boson sampler. Although we worked with a boson sampler, we believe that this novel formulation is relevant to other quantum devices.
This work shows that a good embedding for combinatorial optimisation problems can solve larger problems with the same quantum computing resource. The flexibility of boson sampling quantum devices is a powerful asset in solving combinatorial optimisation problem, because it enables formulations where the output string is always mapped to a valid solution, avoiding the need for penalties.  [68] arXiv:2406.14285 [pdf, html, other]

Title: A Survey of Methods for Mitigating Barren Plateaus for Parameterized Quantum CircuitsComments: 18 pagesSubjects: Quantum Physics (quantph); Emerging Technologies (cs.ET)
Barren Plateaus are a formidable challenge for hybrid quantumclassical algorithms that lead to flat plateaus in the loss function landscape making it difficult to take advantage of the expressive power of parameterized quantum circuits with gradientbased methods. Like in classical neural network models, parameterized quantum circuits suffer the same vanishing gradient issue due to large parameter spaces with nonconvex landscapes. In this review, we present an overview of the different genesis for barren plateaus, mathematical formalisms of common themes around barren plateaus, and dives into gradients. The central objective is to provide a conceptual perspective between classical and quantum interpretations of vanishing gradients as well as dive into techniques involving cost functions, entanglement, and initialization strategies to mitigate barren plateaus. Addressing barren plateaus paves the way towards feasibility of many classically intractable applications for quantum simulation, optimization, chemistry, and quantum machine learning.
 [69] arXiv:2406.14330 [pdf, html, other]

Title: Promise of Graph Sparsification and Decomposition for Noise Reduction in QAOA: Analysis for TrappedIon CompilationsSubjects: Quantum Physics (quantph); Data Structures and Algorithms (cs.DS); Optimization and Control (math.OC)
We develop new approximate compilation schemes that significantly reduce the expense of compiling the Quantum Approximate Optimization Algorithm (QAOA) for solving the MaxCut problem. Our main focus is on compilation with trappedion simulators using Pauli$X$ operations and alltoall Ising Hamiltonian $H_\text{Ising}$ evolution generated by MolmerSorensen or optical dipole force interactions, though some of our results also apply to standard gatebased compilations. Our results are based on principles of graph sparsification and decomposition; the former reduces the number of edges in a graph while maintaining its cut structure, while the latter breaks a weighted graph into a small number of unweighted graphs. Though these techniques have been used as heuristics in various hybrid quantum algorithms, there have been no guarantees on their performance, to the best of our knowledge. This work provides the first provable guarantees using sparsification and decomposition to improve quantum noise resilience and reduce quantum circuit complexity.
For quantum hardware that uses edgebyedge QAOA compilations, sparsification leads to a direct reduction in circuit complexity. For trappedion quantum simulators implementing alltoall $H_\text{Ising}$ pulses, we show that for a $(1\epsilon)$ factor loss in the MaxCut approximation ($\epsilon>0)$, our compilations improve the (worstcase) number of $H_\text{Ising}$ pulses from $O(n^2)$ to $O(n\log(n/\epsilon))$ and the (worstcase) number of Pauli$X$ bit flips from $O(n^2)$ to $O\left(\frac{n\log(n/\epsilon)}{\epsilon^2}\right)$ for $n$node graphs. We demonstrate significant reductions in noise are obtained in our new compilation approaches using theory and numerical calculations for trappedion hardware. We anticipate these approximate compilation techniques will be useful tools in a variety of future quantum computing experiments.  [70] arXiv:2406.14334 [pdf, html, other]

Title: The BoseMarlettoVedral proposal in different frames of reference and the quantum nature of gravityComments: 5 pages, 3 figuresSubjects: Quantum Physics (quantph); General Relativity and Quantum Cosmology (grqc)
Observing spatial entanglement in the BoseMarlettoVedral (BMV) experiment would demonstrate the existence of nonclassical properties of the gravitational field. We show that the special relativistic invariance of the linear regime of general relativity implies that all the components of the gravitational potential must be nonclassical. This is simply necessary in order to describe the BMV entanglement consistently across different inertial frames of reference. On the other hand, we show that the entanglement in accelerated frames could differ from that in stationary frames.
 [71] arXiv:2406.14348 [pdf, other]

Title: Nonstabilizerness in kineticallyconstrained Rydberg atom arraysComments: 15 pages, 7 figuresSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas); Strongly Correlated Electrons (condmat.strel)
Nonstabilizer states are a fundamental resource for universal quantum computation. However,despite broad significance in quantum computing, the emergence of "manybody" nonstabilizerness in interacting quantum systems remains poorly understood due to its analytical intractability. Here we show that Rydberg atom arrays provide a natural reservoir of nonstabilizerness that extends beyond single qubits and arises from quantum correlations engendered by the Rydberg blockade. We demonstrate that this nonstabilizerness can be experimentally accessed in two complementary ways, either by performing quench dynamics or via adiabatic ground state preparation. Using the analytical framework based on matrix product states, we explain the origin of Rydberg nonstabilizerness via a quantum circuit decomposition of the wave function.
 [72] arXiv:2406.14352 [pdf, html, other]

Title: Measuring the Evolution of Entanglement in Compton ScatteringIgor Tkachev, Sultan Musin, Dzhonrid Abdurashitov, Alexander Baranov, Fedor Guber, Alexander Ivashkin, Alexander StrizhakComments: 11 pages, 8 figuresSubjects: Quantum Physics (quantph)
The evolution of the entanglement measure during Compton scattering is studied. Our analytical results show that the corresponding measure coincides with the concurrence of the twoqubit state arising after scattering. The state never collapses to a separable one, contrary to what was previously assumed. The behavior of quantum entanglement during scattering is identical to the behavior of initially classically correlated photons up to a constant factor equal to two. This is consistent with local quantum field theory, and "spooky action at a distance" is not required to explain the change in state of nonlocally entangled qubits during the measurement of one of them. Our dedicated experiment with annihilation photons confirms these results and explains the "Puzzle of Decoherence" observed recently.
 [73] arXiv:2406.14386 [pdf, html, other]

Title: Teleportation with Embezzling CatalystsJunjing Xing, Yuqi Li, Dengke Qu, Lei Xiao, Zhaobing Fan, Haitao Ma, Peng Xue, Kishor Bharti, Dax Enshan Koh, Yunlong XiaoComments: 19 pages, 11 figures. Comments welcome!Subjects: Quantum Physics (quantph)
Quantum teleportation is the process of transferring quantum information using classical communication and preshared entanglement. This process can benefit from the use of catalysts, which are ancillary entangled states that can enhance teleportation without being consumed. While chemical catalysts undergoing deactivation invariably exhibit inferior performance compared to those unaffected by deactivation, quantum catalysts, termed embezzling catalysts, that are subject to deactivation, may surprisingly outperform their nondeactivating counterparts. In this work, we present teleportation protocols with embezzling catalyst that can achieve arbitrarily high fidelity, namely the teleported state can be made arbitrarily close to the original state, with finitedimensional embezzling catalysts. We show that some embezzling catalysts are universal, meaning that they can improve the teleportation fidelity for any preshared entanglement. We also explore methods to reduce the dimension of catalysts without increasing catalyst consumption, an essential step towards realizing quantum catalysis in practice.
 [74] arXiv:2406.14395 [pdf, html, other]

Title: Communication with Quantum CatalystsYuqi Li, Junjing Xing, Dengke Qu, Lei Xiao, Zhaobing Fan, ZhuJun Zheng, Haitao Ma, Peng Xue, Kishor Bharti, Dax Enshan Koh, Yunlong XiaoComments: 16 pages, 9 figures. Comments welcome!Subjects: Quantum Physics (quantph)
Communication is essential for advancing science and technology. Quantum communication, in particular, benefits from the use of catalysts. During the communication process, these catalysts enhance performance while remaining unchanged. Although chemical catalysts that undergo deactivation typically perform worse than those that remain unaffected, quantum catalysts, referred to as embezzling catalysts, can surprisingly outperform their nondeactivating counterparts despite experiencing slight alterations. In this work, we employ embezzling quantum catalysts to enhance the transmission of both quantum and classical information. Our results reveal that using embezzling catalysts augments the efficiency of information transmission across noisy quantum channels, ensuring a nonzero catalytic channel capacity. Furthermore, we introduce catalytic superdense coding, demonstrating how embezzling catalysts can enhance the transmission of classical information. Finally, we explore methods to reduce the dimensionality of catalysts, a step toward making quantum catalysis a practical reality.
 [75] arXiv:2406.14411 [pdf, html, other]

Title: Performance and scaling analysis of variational quantum simulationSubjects: Quantum Physics (quantph)
We present an empirical analysis of the scaling of the minimal quantum circuit depth required for a variational quantum simulation (VQS) method to obtain a solution to the time evolution of a quantum system within a predefined error tolerance. In a comparison against a nonvariational method based on Trotterized time evolution, we observe a better scaling of the depth requirements using the VQS approach with respect to both the size of the system and the simulated time. Results are also put into perspective by discussing the corresponding classical complexity required for VQS. Our results allow us to identify a possible advantage region for VQS over Trotterization.
 [76] arXiv:2406.14445 [pdf, other]

Title: Highthreshold, lowoverhead and singleshot decodable faulttolerant quantum memoryComments: 16 pages, 10 figuresSubjects: Quantum Physics (quantph)
We present a new family of quantum lowdensity paritycheck codes, which we call radial codes, obtained from the lifted product of a specific subset of classical quasicyclic codes. The codes are defined using a pair of integers $(r,s)$ and have parameters $[\![2r^2s,2(r1)^2,\leq2s]\!]$, with numerical studies suggesting averagecase distance linear in $s$. In simulations of circuitlevel noise, we observe comparable error suppression to surface codes of similar distance while using approximately five times fewer physical qubits. This is true even when radial codes are decoded using a singleshot approach, which can allow for faster logical clock speeds and reduced decoding complexity. We describe an intuitive visual representation, canonical basis of logical operators and optimallength stabiliser measurement circuits for these codes, and argue that their error correction capabilities, tunable parameters and small size make them promising candidates for implementation on nearterm quantum devices.
 [77] arXiv:2406.14448 [pdf, html, other]

Title: Polarisationinsensitive state preparation for trappedion hyperfine qubitsSubjects: Quantum Physics (quantph)
Quantum state preparation for trappedion qubits often relies on highquality circularlypolarised light, which may be difficult to achieve with chipbased integrated optics technology. We propose and implement a hybrid optical/microwave scheme for intermediatefield hyperfine qubits which instead relies on frequency selectivity. Experimentally, we achieve $99.94\%$ fidelity for linearlypolarised ($\sigma^+$/$\sigma^$) light, using $^{43}$Ca$^+$ at 28.8 mT. We find that the fidelity remains above $99.8\%$ for a mixture of all polarisations ($\sigma^+$/$\sigma^$/$\pi$). We calculate that the method is capable of $99.99\%$ fidelity in $^{43}$Ca$^+$, and even higher fidelities in heavier ions such as $^\text{137}$Ba$^\text{+}$.
 [78] arXiv:2406.14461 [pdf, html, other]

Title: Generation of manybody entanglement by collective coupling of atom pairs to cavity photonsComments: 5+11 pages, 2 figuresSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas)
The generation of manybody entangled states in atomic samples should be fast, as this process always involves a subtle interplay between desired quantum effects and unwanted decoherence. Here we identify a controllable and scalable catalyst that allows metrologically useful entangled states to be generated at a high rate. This is achieved by immersing a collection of bosonic atoms, trapped in a doublewell potential, in an optical cavity. In the dispersive regime, cavity photons collectively couple pairs of atoms in their ground state to a molecular state, effectively generating, photonnumber dependent atomatom interactions. These effective interactions entangle atoms at a rate that strongly scales with both the number of photons and the number of atoms. As a consequence, the characteristic time scale of entanglement formation can be much shorter than for bare atomatom interactions, effectively eliminating the decoherence due to photon losses. Here, the control of the entanglement generation rate does not require the use of Feshbach resonances, where magnetic field fluctuations can contribute to decoherence. Our protocol may find applications in future quantum sensors or other systems where controllable and scalable manybody entanglement is desired.
 [79] arXiv:2406.14484 [pdf, html, other]

Title: A twodimensional optomechanical crystal for quantum transductionFelix M. Mayor, Sultan Malik, André G. Primo, Samuel Gyger, Wentao Jiang, Thiago P. M. Alegre, Amir H. SafaviNaeiniComments: 13 pages, 4 main figuresSubjects: Quantum Physics (quantph); Optics (physics.optics)
Integrated optomechanical systems are one of the leading platforms for manipulating, sensing, and distributing quantum information. The temperature increase due to residual optical absorption sets the ultimate limit on performance for these applications. In this work, we demonstrate a twodimensional optomechanical crystal geometry, named \textbf{bdagger}, that alleviates this problem through increased thermal anchoring to the surrounding material. Our mechanical mode operates at 7.4 GHz, well within the operation range of standard cryogenic microwave hardware and piezoelectric transducers. The enhanced thermalization combined with the large optomechanical coupling rates, $g_0/2\pi \approx 880~\mathrm{kHz}$, and high optical quality factors, $Q_\text{opt} = 2.4 \times 10^5$, enables the groundstate cooling of the acoustic mode to phononic occupancies as low as $n_\text{m} = 0.35$ from an initial temperature of 3 kelvin, as well as entering the optomechanical strongcoupling regime. Finally, we perform pulsed sideband asymmetry of our devices at a temperature below 10 millikelvin and demonstrate groundstate operation ($n_\text{m} < 0.45$) for repetition rates as high as 3 MHz. Our results extend the boundaries of optomechanical system capabilities and establish a robust foundation for the next generation of microwavetooptical transducers with entanglement rates overcoming the decoherence rates of stateoftheart superconducting qubits.
 [80] arXiv:2406.14501 [pdf, html, other]

Title: Quantum limits of superconductingphotonic links and their extension to mmwavesComments: 14 pages, 8 figuresSubjects: Quantum Physics (quantph)
Photonic addressing of superconducting circuits has been proposed to overcome wiring complexity and heat load challenges, but superconductingphotonic links suffer from an efficiencynoise tradeoff that limits scalability. This tradeoff arises because increasing power conversion efficiency requires reducing optical power, which makes the converted signal susceptible to shot noise. We analyze this tradeoff and find the infidelity of qubit gates driven by photonic signals scales inversely with the number of photons used, and therefore the power efficiency of the converter. While methods like nonlinear detection or squeezed light could mitigate this effect, we consider generating higher frequency electrical signals, such as millimeterwaves (100 GHz), using laser light. At these higher frequencies, circuits have higher operating temperatures and cooling power budgets. We demonstrate an opticallydriven cryogenic millimeterwave source with a power efficiency of $10^{4}$ that can generate ${1}~\mathrm{\mu W}$ of RF power at 80 GHz with 1500 thermal photons of added noise at 4 K. Using this source, we perform frequencydomain spectroscopy of superconducting NbTiN resonators at 8090 GHz. Our results show a promising approach to alleviate the efficiencynoise constraints on opticallydriven superconducting circuits while leveraging the benefits of photonic signal delivery. Further optimization of power efficiency and noise at high frequencies could make photonic control of superconducting qubits viable at temperatures exceeding 1 kelvin.
 [81] arXiv:2406.14527 [pdf, html, other]

Title: Ambiguity Clustering: an accurate and efficient decoder for qLDPC codesSubjects: Quantum Physics (quantph)
Error correction allows a quantum computer to preserve a state long beyond the decoherence time of its physical qubits by encoding logical qubits in a larger number of physical qubits. The leading proposal for a scheme of quantum error correction is based on the surface code, but several recently proposed quantum lowdensity parity check (qLDPC) codes allow more logical information to be encoded in significantly fewer physical qubits. Key to any scheme of quantum error correction is the decoder, an algorithm that estimates the error state of the qubits from the results of syndrome measurements performed on them. The surface code has a variety of fast and accurate decoders, but the stateoftheart decoder for general qLDPC codes, BPOSD, has a high computational complexity. Here we introduce Ambiguity Clustering (AC), an algorithm which seeks to divide the measurement data into clusters which are decoded independently. We benchmark AC on the recently proposed bivariate bicycle codes and find that, at physically realistic error rates, AC is between one and three orders of magnitude faster than BPOSD with no reduction in logical fidelity. Our CPU implementation of AC is already fast enough to decode the 144qubit Gross code in real time for neutral atom and trapped ion systems.
New submissions for Friday, 21 June 2024 (showing 81 of 81 entries )
 [82] arXiv:2406.08430 (crosslist from math.CO) [pdf, html, other]

Title: Testing Quantum and Simulated Annealers on the Drone Delivery Packing ProblemComments: 16 pages, 6 figures, 7 tablesSubjects: Combinatorics (math.CO); Optimization and Control (math.OC); Quantum Physics (quantph)
Using drones to perform humanrelated tasks can play a key role in various fields, such as defense, disaster response, agriculture, healthcare, and many others. The drone delivery packing problem (DDPP) arises in the context of logistics in response to an increasing demand in the delivery process along with the necessity of lowering human intervention. The DDPP is usually formulated as a combinatorial optimization problem, aiming to minimize drone usage with specific battery constraints while ensuring timely consistent deliveries with fixed locations and energy budget. In this work, we propose two alternative formulations of the DDPP as a quadratic unconstrained binary optimization (QUBO) problem, in order to test the performance of classical and quantum annealing (QA) approaches. We perform extensive experiments showing the advantages as well as the limitations of quantum annealers for this optimization problem, as compared to simulated annealing (SA) and classical stateoftheart commercial tools for global optimization.
 [83] arXiv:2406.12962 (crosslist from condmat.strel) [pdf, html, other]

Title: Gauging modulated symmetries: KramersWannier dualities and noninvertible reflectionsComments: 67 pagesSubjects: Strongly Correlated Electrons (condmat.strel); High Energy Physics  Theory (hepth); Mathematical Physics (mathph); Quantum Physics (quantph)
Modulated symmetries are internal symmetries that act in a nonuniform, spatially modulated way and are generalizations of, for example, dipole symmetries. In this paper, we systematically study the gauging of finite Abelian modulated symmetries in ${1+1}$ dimensions. Working with local Hamiltonians of spin chains, we explore the dual symmetries after gauging and their potential new spatial modulations. We establish sufficient conditions for the existence of an isomorphism between the modulated symmetries and their dual, naturally implemented by lattice reflections. For instance, in systems of prime qudits, translation invariance guarantees this isomorphism. For nonprime qudits, we show using techniques from ring theory that this isomorphism can also exist, although it is not guaranteed by lattice translation symmetry alone. From this isomorphism, we identify new KramersWannier dualities and construct related noninvertible reflection symmetry operators using sequential quantum circuits. Notably, this noninvertible reflection symmetry exists even when the system lacks ordinary reflection symmetry. Throughout the paper, we illustrate these results using various simple toy models.
 [84] arXiv:2406.12981 (crosslist from condmat.quantgas) [pdf, html, other]

Title: Quantum geometry of bosonic Bogoliubov quasiparticlesComments: 7+21 pages, 4 figuresSubjects: Quantum Gases (condmat.quantgas); Mesoscale and Nanoscale Physics (condmat.meshall); Quantum Physics (quantph)
Topological and geometrical features arising in bosonic Bogoliubovde Gennes (BdG) systems have mainly been studied by utilizing a generalized symplectic version of the Berry curvature and related Chern numbers. Here, we propose a symplectic quantum geometric tensor (SQGT), whose imaginary part leads to the previously studied symplectic Berry curvature, while the real part gives rise to a symplectic quantum metric, providing a natural distance measure in the space of bosonic Bogoliubov modes. We propose how to measure all components of the SQGT by extracting excitation rates in response to periodic modulations of the systems' parameters. Moreover, we connect the symplectic Berry curvature to a generalized symplectic anomalous velocity term for Bogoliubov Bloch wave packets. We test our results for a bosonic BogoliubovHaldane model.
 [85] arXiv:2406.12990 (crosslist from hepth) [pdf, other]

Title: Universal EarlyTime Growth in Quantum Circuit ComplexityComments: 32 pagesSubjects: High Energy Physics  Theory (hepth); Quantum Physics (quantph)
We show that quantum circuit complexity for the unitary time evolution operator of any timeindependent Hamiltonian is linear in time at early times, independent of any choices of the fundamental gates or cost metric. Deviations from linear earlytime growth arise from the commutation algebra of the gates and are manifestly negative for any circuit, decreasing the linear growth rate and leading to a bound on the growth rate of complexity of a circuit at early times. We illustrate this general result by applying it to qubit and harmonic oscillator systems, including the coupled and anharmonic oscillator. By discretizing free and interacting scalar field theories on a lattice, we are also able to extract the earlytime behavior and dependence on the lattice spacing of complexity of these field theories in the continuum limit, demonstrating how this approach applies to systems that have been previously difficult to study using existing techniques for quantum circuit complexity.
 [86] arXiv:2406.13003 (crosslist from physics.plasmph) [pdf, html, other]

Title: Simulating nonlinear optical processes on a superconducting quantum deviceYuan Shi, Bram Evert, Amy F. Brown, Vinay Tripathi, Eyob A. Sete, Vasily Geyko, Yujin Cho, Jonathan L DuBois, Daniel Lidar, Ilon Joseph, Matt ReagorComments: 26 pages, 5 figuresSubjects: Plasma Physics (physics.plasmph); Quantum Physics (quantph)
Simulating plasma physics on quantum computers is difficult, because most problems of interest are nonlinear, but quantum computers are not naturally suitable for nonlinear operations. In weakly nonlinear regimes, plasma problems can be modeled as wavewave interactions. In this paper, we develop a quantization approach to convert nonlinear wavewave interaction problems to Hamiltonian simulation problems. We demonstrate our approach using two qubits on a superconducting device. Unlike a photonic device, a superconducting device does not naturally have the desired interactions in its native Hamiltonian. Nevertheless, Hamiltonian simulations can still be performed by decomposing required unitary operations into native gates. To improve experimental results, we employ a range of error mitigation techniques. Apart from readout error mitigation, we use randomized compilation to transform undiagnosed coherent errors into wellbehaved stochastic Pauli channels. Moreover, to compensate for stochastic noise, we rescale exponentially decaying probability amplitudes using rates measured from cycle benchmarking. We carefully consider how different choices of productformula algorithms affect the overall error and show how a tradeoff can be made to best utilize limited quantum resources. This study provides a point example of how plasma problems may be solved on nearterm quantum computing platforms.
 [87] arXiv:2406.13058 (crosslist from physics.histph) [pdf, html, other]

Title: Quantum Systems Other Than the UniverseSubjects: History and Philosophy of Physics (physics.histph); Quantum Physics (quantph)
How should we interpret physical theories, and especially quantum theory, if we drop the assumption that we should treat it as an exact description of the whole Universe? I expound and develop the claim that physics is about the study of autonomous, but not necessarily isolated, dynamical systems, and that when applied to quantum mechanics this entails that in general we should take quantum systems as having mixed states and nonunitary dynamics. I argue that nonetheless unitary dynamics continues to have a special place in physics, via the empiricallywellsupported reductionist principles that nonunitarity is to be explained by restriction to a subsystem of a larger unitary system and that microscopic physics is governed by unitary and largely known dynamics. I contrast this position with the `Open Systems View' advocated recently by Michael Cuffaro and Stephan Hartmann.
 [88] arXiv:2406.13416 (crosslist from grqc) [pdf, html, other]

Title: Influence of thermal bath on PancharatnamBerry phase in an accelerated frameComments: Latex, 7 pages, 2 figuresSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth); Quantum Physics (quantph)
A uniformly accelerated atom captures PancharatnamBerry phase in its quantum state and the phase factor depends on the vacuum fluctuation of the background quantum fields. We observe that the thermal nature of the fields further affects the induced phase. Interestingly the induced phase captures the exchange symmetry between the Unruh and real thermal baths. This observation further supports the claim that the Unruh thermal bath mimics a real thermal bath. Moreover for certain values of system parameters and at high temperature, the phase is enhanced compared to zero temperature situation. However the required temperature to observe the phase experimentally is so high that the detection of Unruh effect through this is not possible within the current technology.
 [89] arXiv:2406.13545 (crosslist from physics.optics) [pdf, html, other]

Title: Optimal Diffractive Focusing of Quantum WavesSubjects: Optics (physics.optics); Quantum Physics (quantph)
Following the familiar analogy between the optical paraxial wave equation and the Schrödinger equation, we derive the optimal, realvalued wave function for focusing in one and two space dimensions without the use of any phase component. We compare and contrast the focusing parameters of the optimal waves with those of other diffractive focusing approaches, such as Fresnel zones. Moreover, we experimentally demonstrate these focusing properties on optical beams using both reflective and transmissive liquid crystal devices. Our results provide an alternative direction for focusing waves where phase elements are challenging to implement, such as for Xrays, THz radiation, and electron beams.
 [90] arXiv:2406.13740 (crosslist from condmat.suprcon) [pdf, html, other]

Title: Kinetic Inductance, Quantum Geometry, and Superconductivity in MagicAngle Twisted Bilayer GrapheneMiuko Tanaka, Joel Îj. Wang, Thao H. Dinh, Daniel RodanLegrain, Sameia Zaman, Max Hays, Bharath Kannan, Aziza Almanakly, David K. Kim, Bethany M. Niedzielski, Kyle Serniak, Mollie E. Schwartz, Kenji Watanabe, Takashi Taniguchi, Jeffrey A. Grover, Terry P. Orlando, Simon Gustavsson, Pablo JarilloHerrero, William D. OliverSubjects: Superconductivity (condmat.suprcon); Mesoscale and Nanoscale Physics (condmat.meshall); Strongly Correlated Electrons (condmat.strel); Quantum Physics (quantph)
The physics of superconductivity in magicangle twisted bilayer graphene (MATBG) is a topic of keen interest in moiré systems research, and it may provide insight into the pairing mechanism of other strongly correlated materials such as high$T_{\mathrm{c}}$ superconductors. Here, we use DCtransport and microwave circuit quantum electrodynamics (cQED) to measure directly the superfluid stiffness of superconducting MATBG via its kinetic inductance. We find the superfluid stiffness to be much larger than expected from conventional singleband Fermi liquid theory; rather, it aligns well with theory involving quantum geometric effects that are dominant at the magic angle. The temperature dependence of the superfluid stiffness exhibits a powerlaw behavior, which contraindicates an isotropic BCS model; instead, the extracted powerlaw exponents indicate an anisotropic superconducting gap, whether interpreted using the conventional anisotropic BCS model or a quantum geometric theory of flatband superconductivity. Moreover, the quadratic dependence of the stiffness on both DC and microwave current is consistent with GinzburgLandau theory. Taken together, these findings strongly suggest a connection between quantum geometry, superfluid stiffness, and unconventional superconductivity in MATBG. Finally, the combined DCmicrowave measurement platform used here is applicable to the investigation of other atomically thin superconductors.
 [91] arXiv:2406.13742 (crosslist from condmat.suprcon) [pdf, html, other]

Title: Superfluid stiffness of twisted multilayer graphene superconductorsAbhishek Banerjee, Zeyu Hao, Mary Kreidel, Patrick Ledwith, Isabelle Phinney, Jeong Min Park, Andrew M. Zimmerman, Kenji Watanabe, Takashi Taniguchi, Robert M Westervelt, Pablo JarilloHerrero, Pavel A. Volkov, Ashvin Vishwanath, Kin Chung Fong, Philip KimSubjects: Superconductivity (condmat.suprcon); Mesoscale and Nanoscale Physics (condmat.meshall); Strongly Correlated Electrons (condmat.strel); Quantum Physics (quantph)
The robustness of the macroscopic quantum nature of a superconductor can be characterized by the superfluid stiffness, $\rho_s$, a quantity that describes the energy required to vary the phase of the macroscopic quantum wave function. In unconventional superconductors, such as cuprates, the lowtemperature behavior of $\rho_s$ drastically differs from that of conventional superconductors due to quasiparticle excitations from gapless points (nodes) in momentum space. Intensive research on the recently discovered magicangle twisted graphene family has revealed, in addition to superconducting states, strongly correlated electronic states associated with spontaneously broken symmetries, inviting the study of $\rho_s$ to uncover the potentially unconventional nature of its superconductivity. Here we report the measurement of $\rho_s$ in magicangle twisted trilayer graphene (TTG), revealing unconventional nodalgap superconductivity. Utilizing radiofrequency reflectometry techniques to measure the kinetic inductive response of superconducting TTG coupled to a microwave resonator, we find a linear temperature dependence of $\rho_s$ at low temperatures and nonlinear Meissner effects in the current bias dependence, both indicating nodal structures in the superconducting order parameter. Furthermore, the doping dependence shows a linear correlation between the zero temperature $\rho_s$ and the superconducting transition temperature $T_c$, reminiscent of Uemura's relation in cuprates, suggesting phasecoherencelimited superconductivity. Our results provide strong evidence for nodal superconductivity in TTG and put strong constraints on the mechanisms of these graphenebased superconductors.
 [92] arXiv:2406.13878 (crosslist from condmat.meshall) [pdf, html, other]

Title: Role of BathInduced ManyBody Interactions in the Dissipative Phases of the SuSchriefferHeeger ModelComments: 17 pages, 7 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Quantum Physics (quantph)
The SuSchriefferHeeger chain is a prototype example of a symmetryprotected topological insulator. Coupling it nonperturbatively to local thermal environments, either through the intercell or the intracell fermion tunneling elements, modifies the topological window. To understand this effect, we employ the recently developed reactioncoordinate polaron transform (RCPT) method, which allows treating systembath interactions at arbitrary strengths. The effective system Hamiltonian, which is obtained via the RCPT, exposes the impact of the baths on the SSH chain through renormalization of tunneling elements and the generation of manybody interaction terms. By performing exact diagonalization and computing the ensemble geometric phase, a topological invariant applicable even to systems at finite temperature, we distinguish the trivial band insulator (BI) from the topological insulator (TI) phases. Furthermore, through the RCPT mapping, we are able to pinpoint the main mechanism behind the extension of the parameter space for the TI or the BI phases (depending on the coupling scheme, intracell or intercell), which is the bathinduced, dimerized, manybody interaction. We also study the effect of onsite staggered potentials on the SSH phase diagram, and discuss extensions of our method to higher dimensions.
 [93] arXiv:2406.13907 (crosslist from physics.atomph) [pdf, html, other]

Title: Observation of full contrast icosahedral BoseEinstein statistics in laser desorbed, buffer gas cooled C$_{60}$Subjects: Atomic Physics (physics.atomph); Chemical Physics (physics.chemph); Quantum Physics (quantph)
The quantum mechanical nature of spherical top molecules is particularly evident at low angular momentum quantum number J. Using infrared spectroscopy on the 8.4$\mu$m rovibrational band of buffer gas cooled $^{12}$C$_{60}$, we observe the hitherto unseen R(J = 0  29) rotational progression, including the complete disappearance of certain transitions due to the molecule's perfect icosahedral symmetry and identical bosonic nuclei. The observation of extremely weak C$_{60}$ absorption is facilitated by a laser desorption C$_{60}$ vapor source, which transfers 1000fold less heat to the cryogenic buffer gas cell than a traditional oven source. This technique paves the way to cooling C$_{60}$ and other large gas phase molecules to much lower temperatures, providing continued advances for spectral resolution and sensitivity.
 [94] arXiv:2406.13959 (crosslist from physics.optics) [pdf, html, other]

Title: Multifrequencyresolved Hanbury BrownTwiss EffectJoseph Ferrantini, Jesse Crawford, Sergei Kulkov, Jakub Jirsa, Aaron Mueninghoff, Lucas Lawrence, Stephen Vintskevich, Tommaso Milanese, Samuel Burri, Ermanno Bernasconi, Claudio Bruschini, Michal Marcisovsky, Peter Svihra, Andrei Nomerotski, Paul Stankus, Edoardo Charbon, Raphael A. AbrahaoSubjects: Optics (physics.optics); Instrumentation and Methods for Astrophysics (astroph.IM); Quantum Physics (quantph)
The Hanbury BrownTwiss (HBT) effect holds a pivotal place in intensity interferometry and gave a seminal contribution to the development of quantum optics. To observe such an effect, both good spectral and timing resolutions are necessary. Most often, the HBT effect is observed for a single frequency at a time, due to limitations in dealing with multifrequencies simultaneously, halting and limiting some applications. Here, we report a fast and datadriven spectrometer built with a onedimensional array of singlephotonsensitive avalanche diodes. We report observing the HBT effect for multifrequencies at the same time. Specifically, we observed the HBT for up to 5 lines of the Ne spectrum, but this can be improved even further. Our work represents a major step to make spectral binning and multifrequencies HBT more widely available. The technology we present can benefit both classical and quantum applications.
 [95] arXiv:2406.13978 (crosslist from condmat.meshall) [pdf, html, other]

Title: Topological Solitons in Squareroot Graphene Nanoribbons Controlled by Electric FieldsHaiyue Huang (1), Mamun Sarker (2), Percy Zahl (3), C. Stephen Hellberg (4), Jeremy Levy (5), Ioannis Petrides (1), Alexander Sinitskii (2), Prineha Narang (1,6) ((1) Division of Physical Sciences, College of Letters and Science, University of California, Los Angeles, California, USA (2) Department of Chemistry, University of Nebraska, Lincoln, Nebraska, USA (3) Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, USA (4) U.S. Naval Research Laboratory, Washington, District of Columbia, USA (5) Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania, USA (6) Department of Electrical and Computer Engineering, University of California, Los Angeles, California, USA)Subjects: Mesoscale and Nanoscale Physics (condmat.meshall); Materials Science (condmat.mtrlsci); Computational Physics (physics.compph); Quantum Physics (quantph)
Graphene nanoribbons (GNRs) are unique quasionedimensional (1D) materials that have garnered a lot of research interest in the field of topological insulators. While the topological phases exhibited by GNRs are primarily governed by their chemical structures, the ability to externally control these phases is crucial for their potential utilization in quantum electronics and spintronics. Here we propose a class of GNRs featured by mirror symmetry and four zigzag segments in a unit cell that has unique topological properties induced and controlled by an externally applied electric field. Their band structures manifest two finite gaps which support topological solitons, as described by an effective squareroot model. To demonstrate the experimental feasibility, we design and synthesize a representative partially zigzag chevrontype GNR (pzcGNR) with the desired zigzag segments using a bottomup approach. Firstprinciples calculations on pzcGNR reveal band inversions at the two finite gaps by switching the direction of the electric field, which is in accordance with predictions from the squareroot Hamiltonian. We show different topological phases can be achieved by controlling the direction of the field and the chemical potential of the system in squareroot GNRs. Consequently, upon adding a stepfunction electric field, solitons states can be generated at the domain wall. We discuss the properties of two types of soliton states, depending on whether the terminating commensurate unit cell is mirror symmetric.
 [96] arXiv:2406.14299 (crosslist from math.OC) [pdf, other]

Title: Symplectic Stiefel manifold: tractable metrics, secondorder geometry and Newton's methodsComments: 41 pages, 5 figures, 7 tablesSubjects: Optimization and Control (math.OC); Numerical Analysis (math.NA); Symplectic Geometry (math.SG); Quantum Physics (quantph)
Optimization under the symplecticity constraint is an approach for solving various problems in quantum physics and scientific computing. Building on the results that this optimization problem can be transformed into an unconstrained problem on the symplectic Stiefel manifold, we construct geometric ingredients for Riemannian optimization with a new family of Riemannian metrics called tractable metrics and develop Riemannian Newton schemes. The newly obtained ingredients do not only generalize several existing results but also provide us with freedom to choose a suitable metric for each problem. To the best of our knowledge, this is the first try to develop the explicit secondorder geometry and Newton's methods on the symplectic Stiefel manifold. For the Riemannian Newton method, we first consider novel operatorvalued formulas for computing the Riemannian Hessian of a~cost function, which further allows the manifold to be endowed with a weighted Euclidean metric that can provide a preconditioning effect. We then solve the resulting Newton equation, as the central step of Newton's methods, directly via transforming it into a~saddle point problem followed by vectorization, or iteratively via applying any matrixfree iterative method either to the operator Newton equation or its saddle point formulation. Finally, we propose a hybrid Riemannian Newton optimization algorithm that enjoys both global convergence and quadratic/superlinear local convergence at the final stage. Various numerical experiments are presented to validate the proposed methods.
 [97] arXiv:2406.14320 (crosslist from hepth) [pdf, html, other]

Title: Anyon condensation in mixedstate topological orderComments: 52 pages, 14 figuresSubjects: High Energy Physics  Theory (hepth); Strongly Correlated Electrons (condmat.strel); Mathematical Physics (mathph); Category Theory (math.CT); Quantum Physics (quantph)
We discuss anyon condensation in mixedstate topological order. The phases were recently conjectured to be classified by premodular fusion categories. Just like anyon condensation in purestate topological order, a bootstrap analysis shows condensable anyons are given by connected étale algebras. We explain how to perform generic anyon condensation including noninvertible anyons and successive condensations. Interestingly, some condensations lead to purestate topological orders. We clarify when this happens. We also compute topological invariants of equivalence classes.
 [98] arXiv:2406.14327 (crosslist from condmat.statmech) [pdf, html, other]

Title: Application of Haldane's statistical correlation theory in classical systemsSubjects: Statistical Mechanics (condmat.statmech); Mathematical Physics (mathph); Data Analysis, Statistics and Probability (physics.dataan); Quantum Physics (quantph)
This letter investigates the application of Haldane's statistical correlation theory in classical systems. A modified statistical correlation theory has been proposed by including nonlinearity into the original theory of Haldane. It is shown that indistinguishability can be introduced as a form of external statistical correlation into distinguishable systems. It is proved that this modified statistical correlation theory can be used to derive classical fractional exclusion statistics (CFES) using maximum entropy methods for a selfcorrelating system. An extended nonlinear correlation model based on power series expansion is also proposed, which can produce various intermediate statistical models.
 [99] arXiv:2406.14392 (crosslist from physics.optics) [pdf, other]

Title: An efficient singlettriplet spin qubit to fiber interface assisted by a photonic crystal cavityKui Wu, Sebastian Kindel, Thomas Descamps, Tobias Hangleiter, Jan Christoph Müller, Rebecca Rodrigo, Florian Merget, Hendrik Bluhm, Jeremy WitzensJournalref: The 25th European Conference on Integrated Optics, Springer Proceedings in Physics 402, pp. 365372, 2024Subjects: Optics (physics.optics); Quantum Physics (quantph)
We introduce a novel optical interface between a singlettriplet spin qubit and a photonic qubit which would offer new prospects for future quantum communication applications. The interface is based on a 220 nm thick GaAs/AlGaAs heterostructure membrane and features a gatedefined singlettriplet qubit, a gatedefined optically active quantum dot, a photonic crystal cavity and a bottom gold reflector. All essential components can be lithographically defined and deterministically fabricated, which greatly increases the scalability of onchip integration. According to our FDTD simulations, the interface provides an overall coupling efficiency of 28.7% into a free space Gaussian beam, assuming an SiO2 interlayer filling the space between the reflector and the membrane. The performance can be further increased to 48.5% by undercutting this SiO2 interlayer below the photonic crystal.
Cross submissions for Friday, 21 June 2024 (showing 18 of 18 entries )
 [100] arXiv:2009.09208 (replaced) [pdf, other]

Title: The quantum Ising chain for beginnersJournalref: SciPost Phys. Lect. Notes 82 (2024)Subjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas)
We present here various techniques to work with clean and disordered quantum Ising chains, for the benefit of students and nonexperts. Starting from the JordanWigner transformation, which maps spin1/2 systems into fermionic ones, we review some of the basic approaches to deal with the superconducting correlations that naturally emerge in this context. In particular, we analyse the form of the ground state and excitations of the model, relating them to the symmetrybreaking physics, and illustrate aspects connected to calculating dynamical quantities, thermal averages, correlation functions and entanglement entropy. A few problems provide simple applications of the techniques.
 [101] arXiv:2204.01426 (replaced) [pdf, html, other]

Title: Empirical adequacy of the time operator canonically conjugate to a Hamiltonian generating translationsComments: Accepted version. The mathematical results are unchanged, but I added substantial explanations of the physical significance. Phys. Scr. (2024)Subjects: Quantum Physics (quantph); Mathematical Physics (mathph); History and Philosophy of Physics (physics.histph)
To admit a canonically conjugate time operator, the Hamiltonian has to be a generator of translations (like the momentum operator generates translations in space), so its spectrum must be unbounded. But the Hamiltonian governing our world is thought to be bounded from below. Also, judging by the number of fields and parameters of the Standard Model, the Hamiltonian seems much more complicated.
In this article I give examples of worlds governed by Hamiltonians generating translations. They can be expressed as a partial derivative operator just like the momentum operator, but when expressed in function of other observables they can exhibit any level of complexity. The examples include any quantum world realizing a standard ideal measurement, any quantum world containing a clock or a free massless fermion, the quantum representation of any deterministic timereversible dynamical system without time loops, and any quantum world that cannot return to a past state.
Such worlds are as sophisticated as our world, but they admit a time operator. I show that, despite having unbounded Hamiltonian, they do not decay to infinite negative energy any more than any quantum or classical world. Since two such quantum systems of the same Hilbert space dimension are unitarily equivalent even if the physical content of their observables is very different, they are concrete counterexamples to Hilbert Space Fundamentalism (HSF). Taking the observables into account removes the ambiguity of HSF and the clock ambiguity problem attributed to the PageWootters formalism, also caused by assuming HSF. These results provide additional motivations to restore the spacetime symmetry in the formulation of Quantum Mechanics and for the PageWootters formalism.  [102] arXiv:2204.04493 (replaced) [pdf, html, other]

Title: Entanglementinvertible channelsComments: 38 pages, many diagrams. Rev 4: Final versionJournalref: J. Math. Phys. 65, 062203 (2024)Subjects: Quantum Physics (quantph); Mathematical Physics (mathph); Operator Algebras (math.OA)
In a wellknown result [Werner2001], Werner classified all tight quantum teleportation and dense coding schemes, showing that they correspond to unitary error bases. Here tightness is a certain dimensional restriction: the quantum system to be teleported and the entangled resource must be of dimension d, and the measurement must have d^2 outcomes.
In this work we generalise this classification so as to remove the dimensional restriction altogether, thereby resolving an open problem raised in that work. In fact, we classify not just teleportation and dense coding schemes, but entanglementreversible channels. These are channels between finitedimensional C*algebras which are reversible with the aid of an entangled resource state, generalising ordinary reversibility of a channel.
In Werner's classification, a bijective correspondence between tight teleportation and dense coding schemes was shown: swapping Alice and Bob's operations turns a teleportation scheme into a dense coding scheme and vice versa. We observe that this property generalises ordinary invertibility of a channel; we call it entanglementinvertibility. We show that entanglementinvertible channels are precisely the quantum bijections previously studied in the setting of quantum combinatorics [Musto2018], which are classified in terms of the representation theory of the quantum permutation group.  [103] arXiv:2208.11698 (replaced) [pdf, html, other]

Title: RateDistortion Theory for Mixed StatesComments: 25 pages, 2 figures. v3: updated with additional observations and notesSubjects: Quantum Physics (quantph); Information Theory (cs.IT)
This paper is concerned with quantum data compression of asymptotically many independent and identically distributed copies of ensembles of mixed quantum states. The encoder has access to a side information system. The figure of merit is percopy or local error criterion. Ratedistortion theory studies the tradeoff between the compression rate and the percopy error. The optimal tradeoff can be characterized by the ratedistortion function, which is the best rate given a certain distortion. In this paper, we derive the ratedistortion function of mixedstate compression. The ratedistortion functions in the entanglementassisted and unassisted scenarios are in terms of a singleletter mutual information quantity and the regularized entanglement of purification, respectively. For the general setting where the consumption of both communication and entanglement are considered, we present the full qubitentanglement rate region. Our compression scheme covers both blind and visible compression models (and other models in between) depending on the structure of the side information system.
 [104] arXiv:2209.09172 (replaced) [pdf, html, other]

Title: Witnessing superpositions of causal orders before the process is completedComments: revised version. theoretical and experimental motivation is clarified. main results unchangedSubjects: Quantum Physics (quantph)
The questions we raise in this letter are as follows: What is the most general representation of a quantum state at a single point in time? Can we adapt the current formalisms to situations where the order of quantum operations is coherently or incoherently superposed? If so, what are the relations between the state at a given time and the uncertainty in the order of events before and after it? Establishing the relationship between twostate vector formalism and pseudodensity operators, we introduce the notion of a singletime pseudostate. The tomographic construction of singletime pseudostates is possible by ideal or weak measurements. We demonstrate that the eigenspectrum obtained from weak measurements enables us to discriminate between some coherent and incoherent superpositions of causal orders in pre and postselected systems before the process is completed. Finally, we discuss some possible experimental realizations in existing photonic setups.
 [105] arXiv:2302.04278 (replaced) [pdf, html, other]

Title: Error Mitigation Thresholds in Noisy Random Quantum CircuitsComments: 11 pages, 4 figuresSubjects: Quantum Physics (quantph); Statistical Mechanics (condmat.statmech)
Extracting useful information from noisy nearterm quantum simulations requires error mitigation strategies. A broad class of these strategies rely on precise characterization of the noise source. \new{We study the robustness of probabilistic error cancellation and tensor network error mitigation when the noise is imperfectly characterized}. We adapt an ImryMa argument to predict the existence of a threshold in the robustness of these error mitigation methods for random spatially local circuits in spatial dimensions $D \geq 2$: noise characterization disorder below the threshold rate allows for error mitigation up to times that scale with the number of qubits. For onedimensional circuits, by contrast, mitigation fails at an $\mathcal{O}(1)$ time for any imperfection in the characterization of disorder. As a result, error mitigation is only a practical method for sufficiently wellcharacterized noise. We discuss further implications for tests of quantum computational advantage, faulttolerant probes of measurementinduced phase transitions, and quantum algorithms in nearterm devices.
 [106] arXiv:2302.14811 (replaced) [pdf, html, other]

Title: qSWIFT: Highorder randomized compiler for Hamiltonian simulationComments: 23 pages, 7 figuresJournalref: PRX Quantum 5, 020330 (2024)Subjects: Quantum Physics (quantph)
Hamiltonian simulation is known to be one of the fundamental building blocks of a variety of quantum algorithms such as its most immediate application, that of simulating manybody systems to extract their physical properties. In this work, we present qSWIFT, a highorder randomized algorithm for Hamiltonian simulation. In qSWIFT, the required number of gates for a given precision is independent of the number of terms in Hamiltonian, while the systematic error is exponentially reduced with regards to the order parameter. In this respect, our qSWIFT is a higherorder counterpart of the previously proposed quantum stochastic drift protocol (qDRIFT), in which the number of gates scales linearly with the inverse of the precision required. We construct the qSWIFT channel and establish a rigorous bound for the systematic error quantified by the diamond norm. qSWIFT provides an algorithm to estimate given physical quantities using a system with one ancilla qubit, which is as simple as other productformulabased approaches such as regular TrotterSuzuki decompositions and qDRIFT. Our numerical experiment reveals that the required number of gates in qSWIFT is significantly reduced compared to qDRIFT. Particularly, the advantage is significant for problems where high precision is required; for example, to achieve a systematic relative propagation error of $10^{6}$, the required number of gates in thirdorder qSWIFT is 1000 times smaller than that of qDRIFT.
 [107] arXiv:2304.01425 (replaced) [pdf, html, other]

Title: A GKP qubit protected by dissipation in a highimpedance superconducting circuit driven by a microwave frequency combLevArcady Sellem, Alain Sarlette, Zaki Leghtas, Mazyar Mirrahimi, Pierre Rouchon, Philippe CampagneIbarcqComments: 66 pages, 20 figures, 1 table. Updated version: reorganization of the paper, several clarifications, new sections about ancilla noise propagation and protected measurement of Pauli operatorsSubjects: Quantum Physics (quantph); Optimization and Control (math.OC)
We propose a novel approach to generate, protect and control GKP qubits. It employs a microwave frequency comb parametrically modulating a Josephson circuit to enforce a dissipative dynamics of a high impedance circuit mode, autonomously stabilizing the finiteenergy GKP code. The encoded GKP qubit is robustly protected against all dominant decoherence channels plaguing superconducting circuits but quasiparticle poisoning. In particular, noise from ancillary modes leveraged for dissipation engineering does not propagate at the logical level. In a stateoftheart experimental setup, we estimate that the encoded qubit lifetime could extend two orders of magnitude beyond the breakeven point, with substantial margin for improvement through progress in fabrication and control electronics. Qubit initialization, readout and control via Clifford gates can be performed while maintaining the code stabilization, paving the way toward the assembly of GKP qubits in a faulttolerant quantum computing architecture.
 [108] arXiv:2305.13992 (replaced) [pdf, html, other]

Title: Liouville Space Neural Network Representation of Density MatricesComments: 13 pages, 9 figures. Updated to published versionJournalref: Phys. Rev. A 109, 062215 (2024)Subjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall)
Neural network quantum states as ansatz wavefunctions have shown a lot of promise for finding the ground state of spin models. Recently, work has been focused on extending this idea to mixed states for simulating the dynamics of open systems. Most approaches so far have used a purification ansatz where a copy of the system Hilbert space is added which when traced out gives the correct density matrix. Here, we instead present an extension of the Restricted Boltzmann Machine which directly represents the density matrix in Liouville space. This allows the compact representation of states which appear in meanfield theory. We benchmark our approach on two different version of the dissipative transverse field Ising model which show our ansatz is able to compete with other stateoftheart approaches.
 [109] arXiv:2307.10327 (replaced) [pdf, html, other]

Title: Adaptive Trotterization for timedependent Hamiltonian quantum dynamics using piecewise conservation lawsComments: 7+5pages, 5+2 figures. Accepted in PRLSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas); Statistical Mechanics (condmat.statmech)
Digital quantum simulation relies on Trotterization to discretize time evolution into elementary quantum gates. On current quantum processors with notable gate imperfections, there is a critical tradeoff between improved accuracy for finer timesteps, and increased error rate on account of the larger circuit depth. We present an adaptive Trotterization algorithm to cope with timedependent Hamiltonians, where we propose a concept of piecewise "conserved" quantities to estimate errors in the time evolution between two (nearby) points in time; these allow us to bound the errors accumulated over the full simulation period. They reduce to standard conservation laws in the case of timeindependent Hamiltonians, for which we first developed an adaptive Trotterization scheme [PRX Quantum 4, 030319]. We validate the algorithm for a timedependent quantum spin chain, demonstrating that it can outperform the conventional Trotter algorithm with a fixed step size at a controlled error.
 [110] arXiv:2307.14441 (replaced) [pdf, html, other]

Title: Dense outputs from quantum simulationsComments: 30 pages. Accepted by Journal of Computational PhysicsSubjects: Quantum Physics (quantph); Numerical Analysis (math.NA)
The quantum dense output problem is the process of evaluating timeaccumulated observables from timedependent quantum dynamics using quantum computers. This problem arises frequently in applications such as quantum control and spectroscopic computation. We present a range of algorithms designed to operate on both early and fully faulttolerant quantum platforms. These methodologies draw upon techniques like amplitude estimation, Hamiltonian simulation, quantum linear Ordinary Differential Equation (ODE) solvers, and quantum Carleman linearization. We provide a comprehensive complexity analysis with respect to the evolution time $T$ and error tolerance $\epsilon$. Our results demonstrate that the linearization approach can nearly achieve optimal complexity $\mathcal{O}(T/\epsilon)$ for a certain type of lowrank dense outputs. Moreover, we provide a linearization of the dense output problem that yields an exact and finitedimensional closure which encompasses the original states. This formulation is related to the Koopman Invariant Subspace theory and may be of independent interest in nonlinear control and scientific machine learning.
 [111] arXiv:2307.14892 (replaced) [pdf, html, other]

Title: A minimal quantum heat pump based on highfrequency driving and nonMarkovianityComments: 9 pages, 5 FiguresJournalref: Phys. Rev. E 109, 064121 (2024)Subjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas); Statistical Mechanics (condmat.statmech)
We propose a minimal setup for a quantum heat pump, consisting of two tunnelcoupled quantum dots, each hosting a single level and each being coupled to a different fermionic reservoir. The working principle relies on both nonMarkovian systembath coupling and driving induced resonant coupling. We describe the system using a reactioncoordinate mapping in combination with FloquetBornMarkov theory and characterize its performance.
 [112] arXiv:2309.08666 (replaced) [pdf, html, other]

Title: Variational Embeddings for Many Body Quantum SystemsComments: 15 pages, 7 figures. The framework has been extended to include embeddings of classical variational methodsSubjects: Quantum Physics (quantph); Other Condensed Matter (condmat.other); Computational Physics (physics.compph)
We propose a variational scheme to represent composite quantum systems using multiple parameterized functions of varying accuracies on both classical and quantum hardware. The approach follows the variational principle over the entire system, and is naturally suited for scenarios where an accurate description is only needed in a smaller subspace. We show how to include quantum devices as highaccuracy solvers on these correlated degrees of freedom, while handling the remaining contributions with a classical device. We demonstrate the effectiveness of the protocol on spin chains and small molecules and provide insights into its accuracy and computational cost.
 [113] arXiv:2309.09625 (replaced) [pdf, html, other]

Title: Exceptional nexus in BoseEinstein condensates with collective dissipationChenhao Wang, Nan Li, Jin Xie, Cong Ding, Zhonghua Ji, Liantuan Xiao, Suotang Jia, Ying Hu, Yanting ZhaoComments: accepted by PRLSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas)
In multistate nonHermitian systems, higherorder exceptional points and exotic phenomena with no analogues in twolevel systems arise. A paradigm is the exceptional nexus (EX), a thirdorder EP as the cusp singularity of exceptional arcs (EAs), that has a hybrid topological nature. Using atomic BoseEinstein condensates to implement a dissipative threestate system, we experimentally realize an EX within a twoparameter space, despite the absence of symmetry. The engineered dissipation exhibits density dependence due to the collective atomic response to resonant light. Based on extensive analysis of the system's decay dynamics, we demonstrate the formation of an EX from the coalescence of two EAs with distinct geometries. These structures arise from the different roles played by dissipation in the strong coupling limit and quantum Zeno regime. Our work paves the way for exploring higherorder exceptional physics in the manybody setting of ultracold atoms.
 [114] arXiv:2309.11825 (replaced) [pdf, html, other]

Title: Unambiguous measurement in an unshielded microscale magnetometer with sensitivity below 1 pT/rHzSubjects: Quantum Physics (quantph)
Cold atom magnetometers exploit a dense ensemble of quanta with long coherence times to realise leading sensitivity on the micrometer scale. Configured as a Ramsey interferometer, a cold atom sensor can approach atom shotnoise limited precision but suffers from fringe ambiguity, producing gross errors when the field falls outside a narrow predefined range. We describe how Hilbertdemodulated optical magnetometry can be realised on cold atom sensors to provide field measurements both precise and unambiguous. Continuous reconstruction of the Larmor phase allows us to determine the dc magnetic field unambiguously in an unshielded environment, as well as measure ac variation of the field, in a single shot. The ac measurement allows us to characterize, and then neutralise, linesynchronous magnetic interference, extending reconstruction times. Using $1.6 \times 10^6$ $^{87}$Rb atoms in a volume of $(68 \,\mathrm{\mu m})^3$, we measure a test field to be $ 86.0121261(4) \; \mathrm{\mu T}$ in a single shot, achieving dc sensitivity of 380 fT in a duration of 1000 ms. Our results demonstrate that Hilbertdemodulated optical readout yields metrologicallysignificant sensitivity without the fringe ambiguity inherent to Ramsey interferometry.
 [115] arXiv:2310.09189 (replaced) [pdf, html, other]

Title: Adiabatic perturbation theory for twocomponent systems with one heavy componentSubjects: Quantum Physics (quantph); Other Condensed Matter (condmat.other)
Perturbation theory with respect to the kinetic energy of the heavy component of a twocomponent quantum system is introduced. An effective Hamiltonian that is accurate to second order in the inverse heavy mass is derived. It contains a new form of kinetic energy operator with a Hermitian mass tensor and a complexvalued vector potential. All of the potentials in the effective Hamiltonian can be expressed in terms of covariant derivatives and a resolvent operator. The most salient application of the theory is to systems of electrons and nuclei. The accuracy of the theory is verified numerically in a model diatomic molecule and analytically in a vibronic coupling model.
 [116] arXiv:2310.11308 (replaced) [pdf, html, other]

Title: Protocols for counterfactual and twinfield quantum digital signatureComments: 11 pages, 4 figuresJournalref: Phys. Rev. A 109, 032435 (2024)Subjects: Quantum Physics (quantph)
Quantum digital signature (QDS) is the quantum version of its classical counterpart, and can offer security against attacks of repudiation, signature forging and external eavesdropping, on the basis of quantum mechanical nogo principles. Here we propose a QDS scheme based on quantum counterfactuality, which leverages the concept of interactionfree measurement. Employing the idea behind twinfield cryptography, we show how this twoway protocol can be turned into an equivalent noncounterfactual, oneway protocol, that is both more practical and also theoretically helpful in assessing the experimental feasibility of the first protocol. The proposed QDS protocol can be experimentally implemented with current quantum technology.
 [117] arXiv:2311.05529 (replaced) [pdf, html, other]

Title: Informationtheoretic generalization bounds for learning from quantum dataComments: 48+14 pages, 4 figuresSubjects: Quantum Physics (quantph); Computational Complexity (cs.CC); Information Theory (cs.IT); Machine Learning (cs.LG)
Learning tasks play an increasingly prominent role in quantum information and computation. They range from fundamental problems such as state discrimination and metrology over the framework of quantum probably approximately correct (PAC) learning, to the recently proposed shadow variants of state tomography. However, the many directions of quantum learning theory have so far evolved separately. We propose a general mathematical formalism for describing quantum learning by training on classicalquantum data and then testing how well the learned hypothesis generalizes to new data. In this framework, we prove bounds on the expected generalization error of a quantum learner in terms of classical and quantum informationtheoretic quantities measuring how strongly the learner's hypothesis depends on the specific data seen during training. To achieve this, we use tools from quantum optimal transport and quantum concentration inequalities to establish noncommutative versions of decoupling lemmas that underlie recent informationtheoretic generalization bounds for classical machine learning. Our framework encompasses and gives intuitively accessible generalization bounds for a variety of quantum learning scenarios such as quantum state discrimination, PAC learning quantum states, quantum parameter estimation, and quantumly PAC learning classical functions. Thereby, our work lays a foundation for a unifying quantum informationtheoretic perspective on quantum learning.
 [118] arXiv:2311.05544 (replaced) [pdf, html, other]

Title: Towards adiabatic quantum computing using compressed quantum circuitsComments: 13 pages, 10 figuresJournalref: PRX Quantum 5, 020362 (2024)Subjects: Quantum Physics (quantph)
We describe tensor network algorithms to optimize quantum circuits for adiabatic quantum computing. To suppress diabatic transitions, we include counterdiabatic driving in the optimization and utilize variational matrix product operators to represent adiabatic gauge potentials. Traditionally, Trotter product formulas are used to turn adiabatic time evolution into quantum circuits and the addition of counterdiabatic driving increases the circuit depth per time step. Instead, we classically optimize a parameterized quantum circuit of fixed depth to simultaneously capture adiabatic evolution together with counterdiabatic driving over many time steps. The methods are applied to the ground state preparation of quantum Ising chains with transverse and longitudinal fields. We show that the classically optimized circuits can significantly outperform Trotter product formulas. Additionally, we discuss how the approach can be used for combinatorial optimization.
 [119] arXiv:2311.10433 (replaced) [pdf, html, other]

Title: Task Scheduling Optimization from a Tensor Network PerspectiveComments: 8 pages, 4 figuresSubjects: Quantum Physics (quantph); Emerging Technologies (cs.ET)
We present a novel method for task optimization in industrial plants using quantuminspired tensor network technology. This method allows us to obtain the best possible combination of tasks on a set of machines with a set of constraints without having to evaluate all possible combinations. We simulate a quantum system with all possible combinations, perform an imaginary time evolution and a series of projections to satisfy the constraints. We improve its scalability by means of a compression method, an iterative algorithm, and a genetic algorithm, and show the results obtained on simulated cases.
 [120] arXiv:2312.08065 (replaced) [pdf, html, other]

Title: Hubbard physics with Rydberg atoms: using a quantum spin simulator to simulate strong fermionic correlationsJournalref: Phys. Rev. B 109, 2024, 174409Subjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel)
We propose a hybrid quantumclassical method to investigate the equilibrium physics and the dynamics of strongly correlated fermionic models with spinbased quantum processors. Our proposal avoids the usual pitfalls of fermiontospin mappings thanks to a slavespin method which allows to approximate the original Hamiltonian into a sum of selfcorrelated freefermions and spin Hamiltonians. Taking as an example a Rydbergbased analog quantum processor to solve the interacting spin model, we avoid the challenges of variational algorithms or Trotterization methods. We explore the robustness of the method to experimental imperfections by applying it to the halffilled, singleorbital Hubbard model on the square lattice in and out of equilibrium. We show, through realistic numerical simulations of current Rydberg processors, that the method yields quantitatively viable results even in the presence of imperfections: it allows to gain insights into equilibrium Mott physics as well as the dynamics under interaction quenches. This method thus paves the way to the investigation of physical regimes  whether outofequilibrium, doped, or multiorbital  that are difficult to explore with classical processors.
 [121] arXiv:2312.09784 (replaced) [pdf, html, other]

Title: Quantum Algorithm for Solving the Advection Equation using Hamiltonian SimulationSubjects: Quantum Physics (quantph)
A quantum algorithm for solving the advection equation by embedding the discrete timemarching operator into Hamiltonian simulations is presented. Onedimensional advection can be simulated directly since the central finite difference operator for firstorder derivatives is antiHermitian. Here, this is extended to industrially relevant, multidimensional flows with realistic boundary conditions and arbitrary finite difference stencils. A single copy of the initial quantum state is required and the circuit depth grows linearly with the required number of time steps, the sparsity of the timemarching operator and the inverse of the allowable error. Statevector simulations of a scalar transported in a twodimensional channel flow and liddriven cavity configuration are presented as a proof of concept of the proposed approach.
 [122] arXiv:2401.00301 (replaced) [pdf, html, other]

Title: Robustness of Dynamic Quantum Control: Differential Sensitivity BoundSubjects: Quantum Physics (quantph)
Dynamic control via optimized, piecewiseconstant pulses is a common paradigm for openloop control to implement quantum gates. While numerous methods exist for the synthesis of such controls, there are many open questions regarding the robustness of the resulting control schemes in the presence of model uncertainty; unlike in classical control, there are generally no analytical guarantees on the control performance with respect to inexact modeling of the system. In this paper a new robustness measure based on the differential sensitivity of the gate fidelity error to parametric (structured) uncertainties is introduced, and bounds on the differential sensitivity to parametric uncertainties are used to establish performance guarantees for optimal controllers for a variety of quantum gate types, system sizes, and control implementations. Specifically, it is shown how a maximum allowable perturbation over a set of Hamiltonian uncertainties that guarantees a given fidelity error, can be reliably computed. This measure of robustness is inversely proportional to the upper bound on the differential sensitivity of the fidelity error evaluated under nominal operating conditions. Finally, the results show that the nominal fidelity error and differential sensitivity upper bound are positively correlated across a wide range of problems and control implementations, suggesting that in the highfidelity control regime, rather than there being a tradeoff between fidelity and robustness, higher nominal gate fidelities are positively correlated with increased robustness of the controls in the presence of parametric uncertainties.
 [123] arXiv:2401.09134 (replaced) [pdf, html, other]

Title: Dynamic Cooling on Contemporary Quantum ComputersComments: 19 pages, 11 figuresSubjects: Quantum Physics (quantph)
We study the problem of dynamic cooling whereby a target qubit is cooled at the expense of heating up $N1$ further identical qubits, by means of a global unitary operation. A standard backoftheenvelope high temperature estimate establishes that the target qubit temperature can only be dynamically cooled by at most a factor of $1/\sqrt{N}$. Here, we provide the exact expression for the minimum temperature to which the target qubit can be cooled and reveal that there is a crossover from the high initial temperature regime where the scaling is in fact $1/\sqrt{N}$ to a low initial temperature regime where a much faster scaling of $1/N$ occurs. This slow $1/\sqrt{N}$ scaling, which was relevant for early hightemperature NMR quantum computers, is the reason dynamic cooling was dismissed as ineffectual around 20 years ago; the fact that current lowtemperature quantum computers fall in the fast $1/N$ scaling regime, reinstates the appeal of dynamic cooling today. We further show that the associated work cost of cooling is exponentially more advantageous in the low temperature regime. We discuss the implementation of dynamic cooling in terms of quantum circuits and examine the effects of hardware noise. We successfully demonstrate dynamic cooling in a 3qubit system on a real quantum processor. Since the circuit size grows quickly with $N$, scaling dynamic cooling to larger systems on noisy devices poses a challenge. We therefore propose a suboptimal cooling algorithm, whereby relinquishing a small amount of cooling capability results in a drastically reduced circuit complexity, greatly facilitating the implementation of dynamic cooling on nearfuture quantum computers.
 [124] arXiv:2401.16177 (replaced) [pdf, html, other]

Title: Iterative assembly of $^{171}$Yb atom arrays with cavityenhanced optical latticesM.A. Norcia, H. Kim, W.B. Cairncross, M. Stone, A. Ryou, M. Jaffe, M.O. Brown, K. Barnes, P. Battaglino, T.C. Bohdanowicz, A. Brown, K. Cassella, C.A. Chen, R. Coxe, D. Crow, J. Epstein, C. Griger, E. Halperin, F. Hummel, A.M.W. Jones, J.M. Kindem, J. King, K. Kotru, J. Lauigan, M. Li, M. Lu, E. Megidish, J. Marjanovic, M. McDonald, T. Mittiga, J.A. Muniz, S. Narayanaswami, C. Nishiguchi, T. Paule, K.A. Pawlak, L.S. Peng, K.L. Pudenz, D. Rodriguez Perez, A. Smull, D. Stack, M. Urbanek, R.J.M. van de Veerdonk, Z. Vendeiro, L. Wadleigh, T. Wilkason, T.Y. Wu, X. Xie, E. ZalysGeller, X. Zhang, B.J. BloomComments: 8 pages, 6 figuresSubjects: Quantum Physics (quantph); Atomic Physics (physics.atomph)
Assembling and maintaining large arrays of individually addressable atoms is a key requirement for continued scaling of neutralatombased quantum computers and simulators. In this work, we demonstrate a new paradigm for assembly of atomic arrays, based on a synergistic combination of optical tweezers and cavityenhanced optical lattices, and the incremental filling of a target array from a repetitively filled reservoir. In this protocol, the tweezers provide microscopic rearrangement of atoms, while the cavityenhanced lattices enable the creation of large numbers of optical traps with sufficient depth for rapid lowloss imaging of atoms. We apply this protocol to demonstrate neardeterministic filling (99% persite occupancy) of 1225site arrays of optical traps. Because the reservoir is repeatedly filled with fresh atoms, the array can be maintained in a filled state indefinitely. We anticipate that this protocol will be compatible with midcircuit reloading of atoms into a quantum processor, which will be a key capability for running largescale errorcorrected quantum computations whose durations exceed the lifetime of a single atom in the system.
 [125] arXiv:2402.05018 (replaced) [pdf, html, other]

Title: Quantum Tensor Product Decomposition from Choi State TomographyComments: 9+13 pages, 3+1 figuresSubjects: Quantum Physics (quantph)
The Schmidt decomposition is the goto tool for measuring bipartite entanglement of pure quantum states. Similarly, it is possible to study the entangling features of a quantum operation using its operatorSchmidt, or tensor product decomposition. While quantum technological implementations of the former are thoroughly studied, entangling properties on the operator level are harder to extract in the quantum computational framework because of the exponential nature of sample complexity. Here we present an algorithm for unbalanced partitions into a small subsystem and a large one (the environment) to compute the tensor product decomposition of a unitary whose effect on the small subsystem is captured in classical memory while the effect on the environment is accessible as a quantum resource. This quantum algorithm may be used to make predictions about operator nonlocality, effective open quantum dynamics on a subsystem, as well as for finding lowrank approximations and lowdepth compilations of quantum circuit unitaries. We demonstrate the method and its applications on a timeevolution unitary of an isotropic Heisenberg model in two dimensions.
 [126] arXiv:2403.01716 (replaced) [pdf, html, other]

Title: Dynamics of a Generalized Dicke Model for Spin1 AtomsComments: 16 pages, 12 figuresSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas); Atomic Physics (physics.atomph)
The Dicke model is a staple of theoretical cavity Quantum Electrodynamics (cavity QED), describing the interaction between an ensemble of atoms and a single radiation mode of an optical cavity. It has been studied both quantum mechanically and semiclassically for twolevel atoms, and demonstrates a rich variety of dynamics such as phase transitions, phase multistability, and chaos. In this work we explore an open, spin1 Dicke model with independent co and counterrotating coupling terms as well as a quadratic Zeeman shift enabling control over the atomic energylevel structure. We investigate the stability of operator and moment equations under two approximations and show the system undergoes phase transitions. To compliment these results, we relax the aforementioned approximations and investigate the system semiclassically. We show evidence of phase transitions to steadystate and oscillatory superradiance in this semiclassical model, as well as the emergence of chaotic dynamics. The varied and complex behaviours admitted by the model highlights the need to more rigorously map its dynamics.
 [127] arXiv:2403.06377 (replaced) [pdf, html, other]

Title: Adiabatic versus instantaneous transitions from a harmonic oscillator to an inverted oscillatorComments: 18 pages, 6 figures, 101 references, published in: A. Dodonov and C. C. H. Ribeiro (Eds.), Proceedings of the Second International Workshop on Quantum Nonstationary Systems (LF Editorial, Sao Paulo, 2024, ISBN 9786555634464), Chapter 2, pp. 2142; this https URL. arXiv admin note: text overlap with arXiv:2303.08299Subjects: Quantum Physics (quantph); Mathematical Physics (mathph)
We have obtained explicit analytical formulas for the mean energy and its variance (characterizing the energy fluctuations) of a quantum harmonic oscillator with timedependent frequency in the adiabatic regimes after the frequency passes through zero. The behavior of energy turns out to be quite different in two cases: when the frequency remains real and when it becomes imaginary. In the first case, the mean energy always increases when the frequency returns to its initial value, and the increment coefficient is determined by the exponent in the power law of the frequency crossing zero. On the other hand, if the frequency becomes imaginary, the absolute value of mean energy increases exponentially, even in the adiabatic regime, unless the Hamiltonian becomes time independent. Small corrections to the leading terms of simple adiabatic approximate formulas are crucial in this case, due to the unstable nature of the motion.
 [128] arXiv:2403.06391 (replaced) [pdf, html, other]

Title: Towards verifications of Krylov complexityComments: typos and errors are corrected, LaTeX 29pages, no figureJournalref: Progress of Theoretical and Experimental Physics, Volume 2024, Issue 6, June 2024, 063A01,Subjects: Quantum Physics (quantph); High Energy Physics  Theory (hepth); Mathematical Physics (mathph)
Krylov complexity is considered to provide a measure of the growth of operators evolving under Hamiltonian dynamics. The main strategy is the analysis of the structure of Krylov subspace $\mathcal{K}_M(\mathcal{H},\eta)$ spanned by the multiple applications of the Liouville operator $\mathcal{L}$ defined by the commutator in terms of a Hamiltonian $\mathcal{H}$, $\mathcal{L}:=[\mathcal{H},\cdot]$ acting on an operator $\eta$, $\mathcal{K}_M(\mathcal{H},\eta)=\text{span}\{\eta,\mathcal{L}\eta,\ldots,\mathcal{L}^{M1}\eta\}$. For a given inner product $(\cdot,\cdot)$ of the operators, the orthonormal basis $\{\mathcal{O}_n\}$ is constructed from $\mathcal{O}_0=\eta/\sqrt{(\eta,\eta)}$ by Lanczos algorithm. The moments $\mu_m=(\mathcal{O}_0,\mathcal{L}^m\mathcal{O}_0)$ are closely related to the important data $\{b_n\}$ called Lanczos coefficients. I present the exact and explicit expressions of the moments $\{\mu_m\}$ for 16 quantum mechanical systems which are {\em exactly solvable both in the Schrödinger and Heisenberg pictures}. The operator $\eta$ is the variable of the eigenpolynomials. Among them six systems show a clear sign of `noncomplexity' as vanishing higher Lanczos coefficients $b_m=0$, $m\ge3$.
 [129] arXiv:2403.16893 (replaced) [pdf, html, other]

Title: Explanation of the Generalizations of Uncertainty Principle from Coordinate and Momentum Space PeriodicityComments: Modified with new references, np changes in mathematics; version accepted in EPJ PlusSubjects: Quantum Physics (quantph); High Energy Physics  Theory (hepth)
Generalizations of coordinate $x$momentum $p_x$ Uncertainty Principle, with $\Delta x$ and $\Delta p_x$ dependent terms ($\Delta$ denoting standard deviation), $$\Delta x \Delta p_x\geq i\hbar (1+\alpha\Delta p_x^2 +\beta \Delta x^2)$$ have provided rich dividends as a poor person's approach towards Quantum Gravity, because these can introduce coordinate and momentum scales ($\alpha,\beta$ ) that are appealing conceptually. However, these extensions of Uncertainty Principle are purely phenomenological in nature. Apart from the inherent ambiguity in their explicit structures, the introduction of generalized commutations relations compatible with the the uncertainty relations has some drawbacks.
In the present paper we reveal that these generalized Uncertainty Principles can appear in a perfectly natural way, in canonical quantum mechanics, if one assumes a periodic nature in coordinate or momentum space, as the case may be. We bring in to light quite old, (but not so well known), works by Judge and by Judge and Lewis, that explain in detail how a consistent and generalized Uncertainty Principle is induced in the case of angle $\phi$  angular momentum $L_z$, $$\Delta \phi \Delta L_z \geq i\hbar (1 +\nu \Delta \phi^2)$$ purely from a consistent implementation of {\it{periodic}} nature of the angle variable $\phi $, without changing the $\phi, L_z$ canonical commutation relation. {\it{Structurally this is identical to the well known Extended Uncertainty Principle.}} We directly apply this formalism to formulate the $\Delta x \Delta p_x $ Extended Uncertainty Principle. We identify $\beta$ with an observed length scale relevant in astrophysics context. We speculate about the $\alpha$ extension.  [130] arXiv:2404.05936 (replaced) [pdf, html, other]

Title: Learning Symmetric HamiltonianComments: 8 pages, 2 figuresSubjects: Quantum Physics (quantph)
Hamiltonian Learning is a process of recovering system Hamiltonian from measurements, which is a fundamental problem in quantum information processing. In this study, we investigate the problem of learning the symmetric Hamiltonian from its eigenstate. Inspired by the application of group theory in block diagonal secular determination, we have derived a method to determine the number of linearly independent equations about the Hamiltonian unknowns obtained from an eigenstate. This number corresponds to the degeneracy of the associated irreducible representation of the Hamiltonian symmetry group. To illustrate our approach, we examine the XXX Hamiltonian and the XXZ Hamiltonian. We first determine the Hamiltonian symmetry group, then work out the decomposition of irreducible representation, which serves as foundation for analyzing the uniqueness of recovered Hamiltonian. Our numerical findings consistently align with our theoretical analysis.
 [131] arXiv:2404.10044 (replaced) [pdf, html, other]

Title: Variational quantum simulation: a case study for understanding warm startsComments: 9 + 26 pages, 5 + 2 figuresSubjects: Quantum Physics (quantph); Machine Learning (cs.LG); Machine Learning (stat.ML)
The barren plateau phenomenon, characterized by loss gradients that vanish exponentially with system size, poses a challenge to scaling variational quantum algorithms. Here we explore the potential of warm starts, whereby one initializes closer to a solution in the hope of enjoying larger loss variances. Focusing on an iterative variational method for learning shorterdepth circuits for quantum real and imaginary time evolution we conduct a case study to elucidate the potential and limitations of warm starts. We start by proving that the iterative variational algorithm will exhibit substantial (at worst vanishing polynomially in system size) gradients in a small region around the initializations at each timestep. Convexity guarantees for these regions are then established, suggesting trainability for polynomial size timesteps. However, our study highlights scenarios where a good minimum shifts outside the region with trainability guarantees. Our analysis leaves open the question whether such minima jumps necessitate optimization across barren plateau landscapes or whether there exist gradient flows, i.e., fertile valleys away from the plateau with substantial gradients, that allow for training.
 [132] arXiv:2405.04508 (replaced) [pdf, html, other]

Title: Synthetic magnetism enhanced mechanical squeezing in Brillouin optomechanical systemComments: 9 pages, 7 figures. Comments are welcome!Subjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall)
We propose a scheme to generate large amount of mechanical squeezing, far beyond the $\rm{3dB}$ limit, which is based on synthetic magnetism in optomechanical system that hosts a Backward Stimulated Brillouin Scattering (BSBS) process. Our benchmark system consists of an acoustic mode coupled to two optical modes through the BSBS process, and a Duffing mechanical oscillator that couples to the same optical modes through the standard optomechanical radiation pressure. The synthetic magnetism comes from the modulation of the mechanical coupling between the acoustic and the mechanical mode. When there is no synthetic magnetism, a given amount of mechanical squeezing is generated in the system. This squeezing is mainly dependent on the BSBS process, and it is fragile against thermal noise. By switching on the synthetic magnetism, the degree of the generated squeezing is greatly enhanced and goes far beyond the limit of the $\rm{3dB}$. This large magnetism induced squeezing persists even when there is no BSBS process in the system. Moreover, this generated squeezing is robust enough against thermal noise in comparison to the one induced when the synthetic magnetism is off. Furthermore, both the mechanical variance squeezing and effective phonon number exhibit series of peaks and dips depending on the phase modulation of the mechanical coupling. This oscillatory feature is reminiscent of a sudden death and revival of squeezing phenomenon, which can be used to maintain a desired magnitude of squeezing by tuning this phase. Our proposal provides a path toward a flexible scheme that generates large amount of squeezing, far beyond the $\rm{3dB}$ limit. Such a generated squeezed states can be used for quantum applications including quantum information processing, quantum sensing and metrology, and quantum computing.
 [133] arXiv:2405.08136 (replaced) [pdf, other]

Title: Exact Synthesis of Multiqutrit CliffordCyclotomic CircuitsComments: v1: To appear in the proceedings of the 21st International Conference on Quantum Physics and Logic (QPL 2024). Only change to v2: Appendix figures now display. Only change to v3: Fix typo in metadata. Changes to v4: Minor changes to incorporate reviewer comments, edits to bibliographySubjects: Quantum Physics (quantph)
It is known that the matrices that can be exactly represented by a multiqubit circuit over the Toffoli+Hadamard, Clifford+$T$, or, more generally, Cliffordcyclotomic gate set are precisely the unitary matrices with entries in the ring $\mathbb{Z}[1/2, \zeta_k]$, where $k$ is a positive integer that depends on the gate set and $\zeta_k$ is a primitive $2^k$th root of unity. In the present paper, we establish an analogous correspondence for qutrits. We define the multiqutrit Cliffordcyclotomic gate set of degree $3^k$ by extending the classical qutrit gates $X$, $CX$, and $CCX$ with the Hadamard gate $H$ and the $T_k$ gate $T_k=\mathrm{diag}(1,\omega_k, \omega_k^2)$, where $\omega_k$ is a primitive $3^k$th root of unity. This gate set is equivalent to the qutrit Toffoli+Hadamard gate set when $k=1$, and to the qutrit Clifford+$T_k$ gate set when $k>1$. We then prove that a $3^n\times 3^n$ unitary matrix $U$ can be represented by an $n$qutrit circuit over the Cliffordcyclotomic gate set of degree $3^k$ if and only if the entries of $U$ lie in the ring $\mathbb{Z}[1/3,\omega_k]$.
 [134] arXiv:2405.08439 (replaced) [pdf, html, other]

Title: A link between static and dynamical perturbation theoryComments: 9 pages, 4 figures; typos corrected, figure replaced, explanation added; Accepted in New Journal of PhysicsSubjects: Quantum Physics (quantph)
Dynamics, the physical change in time and a pillar of natural sciences, can be regarded as an emergent phenomenon when the system of interest is part of a larger, static one. This "relational approach to time", in which the system's environment provides a temporal reference, does not only provide insight into foundational issues of physics, but holds the potential for a deeper theoretical understanding as it intimately links statics and dynamics. Reinforcing the significance of this connection, we demonstrate, based on recent progress [Phys. Rev. Lett. 131, 140202 (2023)], the role of emergent time as a vital link between timeindependent and timedependent perturbation theory in quantum mechanics. We calculate first order contributions, which are often the most significant, and discuss the issue of degenerate spectra. Based on our results, we envision future applications for the calculation of dynamical phenomena based on a single pure energy eigenstate.
 [135] arXiv:2405.08810 (replaced) [pdf, other]

Title: Quantum computing with QiskitAli JavadiAbhari, Matthew Treinish, Kevin Krsulich, Christopher J. Wood, Jake Lishman, Julien Gacon, Simon Martiel, Paul D. Nation, Lev S. Bishop, Andrew W. Cross, Blake R. Johnson, Jay M. GambettaSubjects: Quantum Physics (quantph); Emerging Technologies (cs.ET)
We describe Qiskit, a software development kit for quantum information science. We discuss the key design decisions that have shaped its development, and examine the software architecture and its core components. We demonstrate an endtoend workflow for solving a problem in condensed matter physics on a quantum computer that serves to highlight some of Qiskit's capabilities, for example the representation and optimization of circuits at various abstraction levels, its scalability and retargetability to new gates, and the use of quantumclassical computations via dynamic circuits. Lastly, we discuss some of the ecosystem of tools and plugins that extend Qiskit for various tasks, and the future ahead.
 [136] arXiv:2406.11957 (replaced) [pdf, html, other]

Title: Linear response theory for cavity QED materialsComments: No significant changes in second version, just a cross reference with another preprintSubjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel)
We present a rigorous framework for linear response theory in cavity QED materials. Our approach leverages the collective coupling between light and matter, drawing parallels with largeN theories in quantum field theory. We derive closed formulas for various responses of both the cavity and the matter. Our theory is validated by recovering established results for the Dicke model and the Quantum Hall Effect. Additionally, we discover novel excitations in quantum magnets, where the cavity binds magnon pairs into localized states.
 [137] arXiv:2406.11971 (replaced) [pdf, html, other]

Title: Cavity QED materials: Comparison and validation of two linear response theories at arbitrary lightmatter coupling strengthsComments: No significant changes in second version, just a cross reference with another preprintSubjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel)
We develop a linear response theory for materials collectively coupled to a cavity that is valid in all regimes of lightmatter coupling, including symmetrybroken phases. We present and compare two different approaches. First, using a coherent path integral formulation for the partition function to obtain thermal Green functions. This approach relies on a saddle point expansion for the action, that can be truncated in the thermodynamic limit. Second, by formulating the equations of motion for the retarded Green functions and solving them. We use a meanfield decoupling of highorder Green functions in order to obtain a closed, solvable system of equations. Both approaches yield identical results in the calculation of response functions for the cavity and material. These are obtained in terms of the bare cavity and material responses. In combination, the two techniques clarify the validity of a meanfield decoupling in correlated lightmatter systems and provide complementary means to compute finitesize corrections to the thermodynamic limit. The theory is formulated for a general model that encompasses most of the systems typically considered in the field of cavity QED materials, within a longwavelength approximation. Finally, we provide a detailed application of the theory to the Quantum Hall effect and to a collection of magnetic models. We validate our predictions against analytical and finitesize exactdiagonalization results.
 [138] arXiv:2406.12008 (replaced) [pdf, html, other]

Title: QCForest: a ClassicalQuantum Algorithm to Provably Speedup Retraining of Random ForestSubjects: Quantum Physics (quantph); Machine Learning (cs.LG)
Random Forest (RF) is a popular treeensemble method for supervised learning, prized for its ease of use and flexibility. Online RF models require to account for new training data to maintain model accuracy. This is particularly important in applications where data is periodically and sequentially generated over time in data streams, such as autodriving systems, and credit card payments. In this setting, performing periodic model retraining with the old and new data accumulated is beneficial as it fully captures possible drifts in the data distribution over time. However, this is unpractical with stateoftheart classical algorithms for RF as they scale linearly with the accumulated number of samples. We propose QCForest, a classicalquantum algorithm designed to timeefficiently retrain RF models in the streaming setting for multiclass classification and regression, achieving a runtime polylogarithmic in the total number of accumulated samples. QCForest leverages Desq, a quantum algorithm for single tree construction and retraining proposed by Kumar et al. by expanding to multiclass classification, as the original proposal was limited to binary classes, and introducing an exact classical method to replace an underlying quantum subroutine incurring a finite error, while maintaining the same polylogarithmic dependence. Finally, we showcase that QCForest achieves competitive accuracy in comparison to stateoftheart RF methods on widely used benchmark datasets with up to 80,000 samples, while significantly speeding up the model retrain.
 [139] arXiv:2406.12358 (replaced) [pdf, html, other]

Title: Asymmetric dynamical localization and precision measurement of BEC micromotionS. Sagar Maurya, J. Bharathi Kannan, Kushal Patel, Pranab Dutta, Korak Biswas, M. S. Santhanam, Umakant D. RapolSubjects: Quantum Physics (quantph)
We show that a BoseEinstein Condensate (BEC) launched with nonzero initial momentum into a periodically kicked optical lattice creates an asymmetrically localized momentum distribution in a moving frame with a small initial current. This asymmetric localization is investigated under two scenarios; (a) when the BEC is in motion in the laboratory frame and, (b) when the optical lattice is in motion in the laboratory frame. The asymmetric features are shown to arise from the earlytime dynamics induced by the broken parity symmetry and, asymptotically, freeze as the dynamical localization stabilizes. The micromotion of BEC is measured using the earlytime asymmetry. In this context, micromotion refers to the extremely low initial velocity of the BEC along the lattice direction. This originates from the jitter when the hybrid trap potential is turned off. By employing BEC in a kicked and moving optical lattice, the asymmetry in earlytime dynamics is measured to precisely characterize and quantify the micromotion phenomena in the quantum system. Micromotion measurement has applications in quantifying systematic shifts and uncertainties in lightpulse interferometers.
 [140] arXiv:2203.16441 (replaced) [pdf, html, other]

Title: Mixed state representability of entropydensity pairsSubjects: Mathematical Physics (mathph); Quantum Physics (quantph)
We show the representability of densityentropy pairs with canonical and grandcanonical states, and we provide bounds on the kinetic energy of the representing states.
 [141] arXiv:2301.04345 (replaced) [pdf, html, other]

Title: SymmetryPreserving Quadratic Lindbladian and Dissipation Driven Topological Transitions in Gaussian StatesComments: 8 pages, 2 figureSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Quantum Gases (condmat.quantgas); Statistical Mechanics (condmat.statmech); Strongly Correlated Electrons (condmat.strel); Quantum Physics (quantph)
The dynamical evolution of an open quantum system can be governed by the Lindblad equation of the density matrix. In this paper, we propose to characterize the density matrix topology by the topological invariant of its modular Hamiltonian. Since the topological classification of such Hamiltonians depends on their symmetry classes, a primary issue we address is determining the requirement for the Lindbladian operators, under which the modular Hamiltonian can preserve its symmetry class during the dynamical evolution. We solve this problem for the fermionic Gaussian state and for the modular Hamiltonian being a quadratic operator of a set of fermionic operators. When these conditions are satisfied, along with a nontrivial topological classification of the symmetry class of the modular Hamiltonian, a topological transition can occur as time evolves. We present two examples of dissipationdriven topological transitions where the modular Hamiltonian lies in the AIII class with U(1) symmetry and the DIII class without U(1) symmetry. By a finite size scaling, we show that this density matrix topology transition occurs at a finite time. We also present the physical signature of this transition.
 [142] arXiv:2305.06373 (replaced) [pdf, html, other]

Title: Spin exchangeenabled quantum simulator for largescale nonAbelian gauge theoriesComments: $15$ pages, $12$ figuresSubjects: Quantum Gases (condmat.quantgas); Strongly Correlated Electrons (condmat.strel); High Energy Physics  Lattice (heplat); Quantum Physics (quantph)
A central requirement for the faithful implementation of largescale lattice gauge theories (LGTs) on quantum simulators is the protection of the underlying gauge symmetry. Recent advancements in the experimental realizations of largescale LGTs have been impressive, albeit mostly restricted to Abelian gauge groups. Guided by this requirement for gauge protection, we propose an experimentally feasible approach to implement largescale nonAbelian $\mathrm{SU}(N)$ and $\mathrm{U}(N)$ LGTs with dynamical matter in $d+1$D, enabled by twobody spinexchange interactions realizing local emergent gaugesymmetry stabilizer terms. We present two concrete proposals for $2+1$D $\mathrm{SU}(2)$ and $\mathrm{U}(2)$ LGTs, including dynamical bosonic matter and induced plaquette terms, that can be readily implemented in current ultracoldmolecule and nextgeneration ultracoldatom platforms. We provide numerical benchmarks showcasing experimentally accessible dynamics, and demonstrate the stability of the underlying nonAbelian gauge invariance. We develop a method to obtain the effective gaugeinvariant model featuring the relevant magnetic plaquette and minimal gaugematter coupling terms. Our approach paves the way towards nearterm realizations of largescale nonAbelian quantum link models in analog quantum simulators.
 [143] arXiv:2306.08529 (replaced) [pdf, other]

Title: SQL2Circuits: Estimating Metrics for SQL Queries with a Quantum Natural Language Processing MethodComments: 15 pages, 13 figures, 2 tablesSubjects: Databases (cs.DB); Machine Learning (cs.LG); Quantum Physics (quantph)
In recent years, advances in quantum computing have led to accelerating research on quantum applications across fields. Here, we introduce a quantum machine learning model as a potential solution to the classical question in database research: the estimation of metrics for SQL queries. This work employs a quantum natural language processing (QNLP)inspired approach for constructing a quantum machine learning model that can classify SQL queries with respect to their cardinalities, costs, and execution times. The model consists of an encoding mechanism and a training phase, including classical and quantum subroutines. The encoding mechanism encodes SQL queries as parametrized quantum circuits. In the training phase, we utilize classical optimization algorithms, such as SPSA and Adam, to optimize the circuit parameters to make predictions about the query metrics. We conclude that our model reaches an accuracy equivalent to that of the QNLP model in the binary classification tasks. Moreover, we extend the previous work by adding 4class classification tasks and compare the cardinality estimation results to the stateoftheart databases. We perform a theoretical analysis of the quantum machine learning model by calculating its expressibility and entangling capabilities. The analysis shows that the model has advantageous properties that make it expressible but also not too complex to be executed on the existing quantum hardware.
 [144] arXiv:2311.16748 (replaced) [pdf, html, other]

Title: Heat Pulses in Electron Quantum OpticsComments: 7+5 pages, 4 figuresJournalref: Phys. Rev. Lett. 132, 256301 (2024)Subjects: Mesoscale and Nanoscale Physics (condmat.meshall); Quantum Physics (quantph)
Electron quantum optics aims to realize ideas from the quantum theory of light with the role of photons being played by charge pulses in electronic conductors. Experimentally, the charge pulses are excited by timedependent voltages, however, one could also generate heat pulses by heating and cooling an electrode. Here, we explore this intriguing idea by formulating a Floquet scattering theory of heat pulses in mesoscopic conductors. The adiabatic emission of heat pulses leads to a heat current that in linear response is given by the thermal conductance quantum. However, we also find a highfrequency component, which ensures that the fluctuationdissipation theorem for heat currents, whose validity has been debated, is fulfilled. The heat pulses are uncharged, and we probe their electronhole content by evaluating the partition noise in the outputs of a quantum point contact. We also employ a HongOuMandel setup to examine if the pulses bunch or antibunch. Finally, to generate an electric current, we use a MachZehnder interferometer that breaks the electronhole symmetry and thereby enables a thermoelectric effect. Our work paves the way for systematic investigations of heat pulses in mesoscopic conductors, and it may stimulate future experiments.
 [145] arXiv:2312.09253 (replaced) [pdf, html, other]

Title: Bayesian Optimization for Robust State Preparation in Quantum ManyBody SystemsComments: 6 + 6 pagesSubjects: Quantum Gases (condmat.quantgas); Quantum Physics (quantph)
New generations of ultracoldatom experiments are continually raising the demand for efficient solutions to optimal control problems. Here, we apply Bayesian optimization to improve a statepreparation protocol recently implemented in an ultracoldatom system to realize a twoparticle fractional quantum Hall state. Compared to manual ramp design, we demonstrate the superior performance of our optimization approach in a numerical simulation  resulting in a protocol that is 10x faster at the same fidelity, even when taking into account experimentally realistic levels of disorder in the system. We extensively analyze and discuss questions of robustness and the relationship between numerical simulation and experimental realization, and how to make the best use of the surrogate model trained during optimization. We find that numerical simulation can be expected to substantially reduce the number of experiments that need to be performed with even the most basic transfer learning techniques. The proposed protocol and workflow will pave the way toward the realization of more complex manybody quantum states in experiments.
 [146] arXiv:2312.14011 (replaced) [pdf, html, other]

Title: Control of threshold voltages in Si/SiGe quantum devices via optical illuminationM. A. Wolfe, Brighton X. Coe, Justin S. Edwards, Tyler J. Kovach, Thomas McJunkin, Benjamin Harpt, D. E. Savage, M. G. Lagally, R. McDermott, Mark Friesen, Shimon Kolkowitz, M. A. ErikssonComments: 8 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Quantum Physics (quantph)
Optical illumination of quantumdot qubit devices at cryogenic temperatures, while not well studied, is often used to recover operating conditions after undesired shocking events or charge injection. Here, we demonstrate systematic threshold voltage shifts in a dopantfree, Si/SiGe field effect transistor using a near infrared (780 nm) laser diode. We find that illumination under an applied gate voltage can be used to set a specific, stable, and reproducible threshold voltage that, over a wide range in gate bias, is equal to that gate bias. Outside this range, the threshold voltage can still be tuned, although the resulting threshold voltage is no longer equal to the applied gate bias during illumination. We present a simple and intuitive model that provides a mechanism for the tunability in gate bias. The model presented also explains why cryogenic illumination is successful at resetting quantum dot qubit devices after undesired charging events.
 [147] arXiv:2403.06040 (replaced) [pdf, html, other]

Title: Implementation and characterization of the dice lattice in the electron quantum simulatorComments: 10 pages, 9 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Quantum Physics (quantph)
Materials featuring touching points, localized states, and flat bands are of great interest in condensed matter and artificial systems due to their implications in topology, quantum geometry, superconductivity, and interactions. In this theoretical study, we propose the experimental realization of the dice lattice with adjustable parameters by arranging carbon monoxide molecules on a twodimensional electron system at a (111) copper surface. First, we develop a theoretical framework to obtain the spectral properties within a nearly free electron approximation and then compare them with tightbinding calculations. Our investigation reveals that the high mobility of Shockley state electrons enables an accurate theoretical description of the artificial lattice using a nextnearestneighbor tightbinding model, resulting in the emergence of a touching point, a quasiflat band, and localized lattice site behavior in the local density of states. Additionally, we present theoretical results for a longwavelength lowenergy model that accounts for nextnearestneighbor hopping terms. Furthermore, we theoretically examine the model's behavior under an external magnetic field by employing Peierl's substitution, a commonly used technique in theoretical physics to incorporate magnetic fields into lattice models. Our theoretical findings suggest that, owing to the exceptional electron mobility, the highly degenerate eigenenergy associated with the AharonovBohm caging mechanism may not manifest in the proposed experiment.
 [148] arXiv:2403.09345 (replaced) [pdf, html, other]

Title: ClassicalQuantum correspondence in Lindblad evolutionComments: Main article by Jeffrey Galkowski and Maciej Zworski with an appendix by Zhen Huang and Maciej Zworski  new appendix with numerical experiments and a new section providing estimates for the HilbertSchmidt norm under Lindblad evolutionSubjects: Mathematical Physics (mathph); Analysis of PDEs (math.AP); Quantum Physics (quantph)
We show that for the Lindblad evolution defined using (at most) quadratically growing classical Hamiltonians and (at most) linearly growing classical jump functions (quantized into jump operators assumed to satisfy certain ellipticity conditions and modeling interaction with a larger system), the evolution of a quantum observable remains close to the classical FokkerPlanck evolution in the HilbertSchmidt norm for times vastly exceeding the Ehrenfest time (the limit of such agreement with no jump operators). The time scale is the same as in the recent papers by HernándezRanardRiedel but the statement and methods are different. The appendix presents numerical experiments illustrating the classical/quantum correspondence in Lindblad evolution and comparing it to the mathematical results.
 [149] arXiv:2404.02998 (replaced) [pdf, html, other]

Title: Dispersive shock waves in a onedimensional dropletbearing environmentSathyanarayanan Chandramouli, Simeon I. Mistakidis, Garyfallia C. Katsimiga, Panayotis G. KevrekidisComments: 15 pages, 9 figuresSubjects: Pattern Formation and Solitons (nlin.PS); Quantum Physics (quantph)
We demonstrate the controllable generation of distinct types of dispersive shockwaves emerging in a quantum droplet bearing environment with the aid of steplike initial conditions. Dispersive regularization of the ensuing hydrodynamic singularities occurs due to the competition between meanfield repulsion and attractive quantum fluctuations. This interplay delineates the dominance of defocusing (hyperbolic) and focusing (elliptic) hydrodynamic phenomena respectively being designated by real and imaginary speed of sound. Specifically, the symmetries of the extended GrossPitaevskii model lead to a threeparameter family, encompassing two densities and a relative velocity, of the underlying Riemann problem utilized herein. Surprisingly, dispersive shock waves persist across the hyperbolictoelliptic threshold, while a plethora of additional wave patterns arise, such as rarefaction waves, traveling dispersive shock waves, (anti)kinks and droplet wavetrains. The classification and characterization of these features is achieved by deploying Whitham modulation theory. Our results pave the way for unveiling a multitude of unexplored coherently propagating waveforms in such attractively interacting mixtures and should be detectable by current experiments.
 [150] arXiv:2404.03651 (replaced) [pdf, html, other]

Title: Multipartite edge modes and tensor networksComments: 49 pages, 78 pages with appendices, 19 figuresSubjects: High Energy Physics  Theory (hepth); Strongly Correlated Electrons (condmat.strel); Quantum Physics (quantph)
Holographic tensor networks model AdS/CFT, but so far they have been limited by involving only systems that are very different from gravity. Unfortunately, we cannot straightforwardly discretize gravity to incorporate it, because that would break diffeomorphism invariance. In this note, we explore a resolution. In low dimensions gravity can be written as a topological gauge theory, which can be discretized without breaking gaugeinvariance. However, new problems arise. Foremost, we now need a qualitatively new kind of "area operator," which has no relation to the number of links along the cut and is instead topological. Secondly, the inclusion of matter becomes trickier. We successfully construct a tensor network both including matter and with this new type of area. Notably, while this area is still related to the entanglement in "edge mode" degrees of freedom, the edge modes are no longer bipartite entangled pairs. Instead they are highly multipartite. Along the way, we calculate the entropy of novel subalgebras in a particular topological gauge theory. We also show that the multipartite nature of the edge modes gives rise to noncommuting area operators, a property that other tensor networks do not exhibit.
 [151] arXiv:2405.10351 (replaced) [pdf, html, other]

Title: Topological phases of extended SuSchriefferHeegerHubbard modelComments: 16 pages, 11 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Quantum Physics (quantph)
Despite extensive studies on the onedimensional SuSchriefferHeegerHubbard (SSHH) model, the variant incorporating nextnearest neighbour hopping remains largely unexplored. Here, we investigate the groundstate properties of this extended SSHH model using the constrainedpath auxiliaryfield quantum Monte Carlo (CPAFQMC) method. We show that this model exhibits rich topological phases, characterized by robust edge states against interaction. We quantify the properties of these edge states by analyzing spin correlation and secondorder Rényi entanglement entropy. The system exhibits longrange spin correlation and nearzero Rényi entropy at halffilling. Besides, there is a longrange antiferromagnetic order at quarterfilling. Interestingly, an external magnetic field disrupts this longrange antiferromagnetic order, restoring longrange spin correlation and nearzero Rényi entropy. Furthermore, our work provides a paradigm studying topological properties in large interacting systems via the CPAFQMC algorithm.
 [152] arXiv:2405.16972 (replaced) [pdf, html, other]

Title: ChipScale PointSource Sagnac Interferometer by PhaseSpace SqueezingSubjects: Atomic Physics (physics.atomph); Instrumentation and Detectors (physics.insdet); Quantum Physics (quantph)
Matterwave interferometry is essential to both science and technology. Phasespace squeezing has been shown to be an advantageous source of atoms, whereby the spread in momentum is decreased. Here, we show that the opposite squeezing may be just as advantageous. As an exemplification, we analyze the effect of such a source on point source atom interferometry (PSI), which enables rotation sensing. We describe how a squeezed PSI (SPSI) increases the sensitivity and dynamic range while facilitating short cycle times and high repetition rates. We present regions in parameter space for which the figures of merit are improved by orders of magnitude and show that under some definition of compactness, the SPSI is superior by more than four orders of magnitude. The SPSI thus enables either enhancing the performance for standard size devices or maintaining the performance while miniaturizing to a chipscale device, opening the door to reallife applications.
 [153] arXiv:2406.03863 (replaced) [pdf, other]

Title: Topological Materials for NearField Radiative Heat TransferAzadeh DidariBader, Seonyeong Kim, Heejin Choi, Sunae Seo, Piyali Biswas, Heejeong Jeong, ChangWon LeeSubjects: Optics (physics.optics); Quantum Physics (quantph)
Topological materials provide a platform that utilizes the geometric characteristics of structured materials to control the flow of waves, enabling unidirectional and protected transmission that is immune to defects or impurities. The topologically designed photonic materials can carry quantum states and electromagnetic energy, benefiting nanolasers or quantum photonic systems. This article reviews recent advances in the topological applications of photonic materials for radiative heat transfer, especially in the near field. When the separation distance between media is considerably smaller than the thermal wavelength, the heat transfer exhibits superPlanckian behavior that surpasses Planck's blackbody predictions. Nearfield thermal radiation in subwavelength systems supporting surface modes has various applications, including nanoscale thermal management and energy conversion. Photonic materials and structures that support topological surface states show immense potential for enhancing or suppressing nearfield thermal radiation. We present various topological effects, such as periodic and quasiperiodic nanoparticle arrays, Dirac and Weyl semimetalbased materials, structures with broken global symmetries, and other topological insulators, on nearfield heat transfer. Also, the possibility of realizing nearfield thermal radiation in such topological materials for alternative thermal management and heat flux guiding in nanoscale systems is discussed based on the existing technology.
 [154] arXiv:2406.04310 (replaced) [pdf, html, other]

Title: Neural Networks Assisted MetropolisHastings for Bayesian Estimation of Critical Exponent on Elliptic Black Hole Solution in 4D Using Quantum Perturbation TheoryComments: V2: 3 extra figures for loss functions on Gaussian proposal distributions are added. Section 4 is modified. 37 pages, 14 figuresSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc); Mathematical Physics (mathph); Quantum Physics (quantph)
It is wellknown that the critical gravitational collapse produces continuous selfsimilar solutions characterized by the Choptuik critical exponent, $\gamma$. We examine the solutions in the domains of the linear perturbation equations, considering the numerical measurement errors. Specifically, we study quantum perturbation theory for the fourdimensional Einsteinaxiondilaton system of the elliptic class of $\text{SL}(2,\mathbb{R})$ transformations. We develop a novel artificial neural networkassisted MetropolisHastings algorithm based on quantum perturbation theory to find the distribution of the critical exponent in a Bayesian framework. Unlike existing methods, this new probabilistic approach identifies the available deterministic solution and explores the range of physically distinguishable critical exponents that may arise due to numerical measurement errors.
 [155] arXiv:2406.05842 (replaced) [pdf, html, other]

Title: Replica symmetry breaking in spin glasses in the replicafree Keldysh formalismComments: 17 pages, 4 figures, submitted versionSubjects: Disordered Systems and Neural Networks (condmat.disnn); Statistical Mechanics (condmat.statmech); Strongly Correlated Electrons (condmat.strel); Mathematical Physics (mathph); Quantum Physics (quantph)
At asymptotically late times ultrametricity can emerge from the persistent slow aging dynamics of the glass phase. We show that this suffices to recover the breaking of replica symmetry in meanfield spin glasses from the late time limit of the time evolution using the Keldysh path integral. This provides an alternative approach to replica symmetry breaking by connecting it rigorously to the dynamic formulation. Stationary spin glasses are thereby understood to spontaneously break thermal symmetry, or the KuboMartinSchwinger relation of a state in global thermal equilibrium. We demonstrate our general statements for the spherical quantum $p$spin model and the quantum SherringtonKirkpatrick model in the presence of transverse and longitudinal fields. In doing so, we also derive their dynamical GinzburgLandau effective Keldysh actions starting from microscopic quantum models.
 [156] arXiv:2406.06063 (replaced) [pdf, html, other]

Title: Enabling LargeScale and HighPrecision Fluid Simulations on NearTerm Quantum ComputersZhaoYun Chen, TengYang Ma, ChuangChao Ye, Liang Xu, MingYang Tan, XiNing Zhuang, XiaoFan Xu, YunJie Wang, TaiPing Sun, Yong Chen, Lei Du, LiangLiang Guo, HaiFeng Zhang, HaoRan Tao, TianLe Wang, XiaoYan Yang, ZeAn Zhao, Peng Wang, Sheng Zhang, Chi Zhang, RenZe Zhao, ZhiLong Jia, WeiCheng Kong, MengHan Dou, JunChao Wang, HuanYu Liu, Cheng Xue, PengJunYi Zhang, ShengHong Huang, Peng Duan, YuChun Wu, GuoPing GuoComments: 31 pages, 10 figuresSubjects: Computational Physics (physics.compph); Quantum Physics (quantph)
Quantum computational fluid dynamics (QCFD) offers a promising alternative to classical computational fluid dynamics (CFD) by leveraging quantum algorithms for higher efficiency. This paper introduces a comprehensive QCFD method, including an iterative method "IterativeQLS" that suppresses error in quantum linear solver, and a subspace method to scale the solution to a larger size. We implement our method on a superconducting quantum computer, demonstrating successful simulations of steady Poiseuille flow and unsteady acoustic wave propagation. The Poiseuille flow simulation achieved a relative error of less than $0.2\%$, and the unsteady acoustic wave simulation solved a 5043dimensional matrix. We emphasize the utilization of the quantumclassical hybrid approach in applications of nearterm quantum computers. By adapting to quantum hardware constraints and offering scalable solutions for largescale CFD problems, our method paves the way for practical applications of nearterm quantum computers in computational science.