Quantum Physics
New submissions
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New submissions for Wed, 1 May 24
- [1] arXiv:2404.19005 [pdf, other]
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Title: Fault-tolerant compiling of classically hard IQP circuits on hypercubesAuthors: Dominik Hangleiter, Marcin Kalinowski, Dolev Bluvstein, Madelyn Cain, Nishad Maskara, Xun Gao, Aleksander Kubica, Mikhail D. Lukin, Michael J. GullansComments: 27 + 20 pages, 13 FiguresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Computational Complexity (cs.CC); Atomic Physics (physics.atom-ph)
Realizing computationally complex quantum circuits in the presence of noise and imperfections is a challenging task. While fault-tolerant quantum computing provides a route to reducing noise, it requires a large overhead for generic algorithms. Here, we develop and analyze a hardware-efficient, fault-tolerant approach to realizing complex sampling circuits. We co-design the circuits with the appropriate quantum error correcting codes for efficient implementation in a reconfigurable neutral atom array architecture, constituting what we call a fault-tolerant compilation of the sampling algorithm. Specifically, we consider a family of $[[2^D , D, 2]]$ quantum error detecting codes whose transversal and permutation gate set can realize arbitrary degree-$D$ instantaneous quantum polynomial (IQP) circuits. Using native operations of the code and the atom array hardware, we compile a fault-tolerant and fast-scrambling family of such IQP circuits in a hypercube geometry, realized recently in the experiments by Bluvstein et al. [Nature 626, 7997 (2024)]. We develop a theory of second-moment properties of degree-$D$ IQP circuits for analyzing hardness and verification of random sampling by mapping to a statistical mechanics model. We provide evidence that sampling from hypercube IQP circuits is classically hard to simulate and analyze the linear cross-entropy benchmark (XEB) in comparison to the average fidelity. To realize a fully scalable approach, we first show that Bell sampling from degree-$4$ IQP circuits is classically intractable and can be efficiently validated. We further devise new families of $[[O(d^D),D,d]]$ color codes of increasing distance $d$, permitting exponential error suppression for transversal IQP sampling. Our results highlight fault-tolerant compiling as a powerful tool in co-designing algorithms with specific error-correcting codes and realistic hardware.
- [2] arXiv:2404.19011 [pdf, other]
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Title: Synthesizing the Born rule with reinforcement learningAuthors: Rodrigo S. Piera, John B. DeBrota, Matthew B. Weiss, Gabriela B. Lemos, Jailson Sales Araújo, Gabriel H. Aguilar, Jacques L. PienaarComments: 10 pages, 5 figuresSubjects: Quantum Physics (quant-ph)
According to the subjective Bayesian interpretation of quantum theory (QBism), quantum mechanics is a tool that an agent would be wise to use when making bets about natural phenomena. In particular, the Born rule is understood to be a decision-making norm, an ideal which one should strive to meet even if usually falling short in practice. What is required for an agent to make decisions that conform to quantum mechanics? Here we investigate how a realistic (hence non-ideal) agent might deviate from the Born rule in its decisions. To do so we simulate a simple agent as a reinforcement-learning algorithm that makes `bets' on the outputs of a symmetric informationally-complete measurement (SIC) and adjusts its decisions in order to maximize its expected return. We quantify how far the algorithm's decision-making behavior departs from the ideal form of the Born rule and investigate the limiting factors. We propose an experimental implementation of the scenario using heralded single photons.
- [3] arXiv:2404.19013 [pdf, ps, other]
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Title: Transitionless Quantum Driving of the Tomonaga-Luttinger LiquidComments: 5+7, 1 figureSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
Shortcuts to adiabaticity (STA) make the fast preparation of many-body states possible, circumventing the limitations of adiabatic strategies. We propose a fast STA protocol for generating interacting states in the Tomonaga-Luttinger liquid by counter-diabatic driving, stirring the dynamics with an auxiliary control field. To this end, we exploit the equivalence between the time-dependent Tomonaga-Luttinger liquid and an ensemble of quantum oscillators with driven mass and frequency. We specify the closed-form expression of the counterdiabatic control and demonstrate its efficiency in suppressing excitations.
- [4] arXiv:2404.19023 [pdf, other]
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Title: Sign problem in tensor network contractionSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
We investigate how the computational difficulty of contracting tensor networks depends on the sign structure of the tensor entries. Using results from computational complexity, we observe that the approximate contraction of tensor networks with only positive entries has lower complexity. This raises the question how this transition in computational complexity manifests itself in the hardness of different contraction schemes. We pursue this question by studying random tensor networks with varying bias towards positive entries. First, we consider contraction via Monte Carlo sampling, and find that the transition from hard to easy occurs when the entries become predominantly positive; this can be seen as a tensor network manifestation of the Quantum Monte Carlo sign problem. Second, we analyze the commonly used contraction based on boundary tensor networks. Its performance is governed by the amount of correlations (entanglement) in the tensor network. Remarkably, we find that the transition from hard to easy (i.e., from a volume law to a boundary law scaling of entanglement) occurs already for a slight bias towards a positive mean, and the earlier the larger the bond dimension is. This is in contrast to both expectations and the behavior found in Monte Carlo contraction. We gain further insight into this early transition from the study of an effective statmech model. Finally, we investigate the computational difficulty of computing expectation values of tensor network wavefunctions, i.e., PEPS, where we find that the complexity of entanglement-based contraction always remains low. We explain this by providing a local transformation which maps PEPS expectation values to a positive-valued tensor network. This not only provides insight into the origin of the observed boundary law entanglement scaling, but also suggests new approaches towards PEPS contraction based on positive decompositions.
- [5] arXiv:2404.19027 [pdf, other]
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Title: Better Optimization of Variational Quantum Eigensolvers by combining the Unitary Block Optimization Scheme with Classical Post-ProcessingComments: 16 pages, 10 figuresSubjects: Quantum Physics (quant-ph); Computational Physics (physics.comp-ph)
Variational Quantum Eigensolvers (VQE) are a promising approach for finding the classically intractable ground state of a Hamiltonian. The Unitary Block Optimization Scheme (UBOS) is a state-of-the-art VQE method which works by sweeping over gates and finding optimal parameters for each gate in the environment of other gates. UBOS improves the convergence time to the ground state by an order of magnitude over Stochastic Gradient Descent (SGD). It nonetheless suffers in both rate of convergence and final converged energies in the face of highly noisy expectation values coming from shot noise. Here we develop two classical post-processing techniques which improve UBOS especially when measurements have large noise. Using Gaussian Process Regression (GPR) we generate artificial augmented data using original data from the quantum computer to reduce the overall error when solving for the improved parameters. Using Double Robust Optimization plus Rejection (DROPR), we prevent outlying data which are atypically noisy from resulting in a a particularly erroneous single optimization step thereby increasing robustness against noisy measurements. Combining these techniques further reduces the final relative error that UBOS reaches by a factor of three without adding additional quantum measurement or sampling overhead. This work further demonstrates that developing techniques which use classical resources to post-process quantum measurement results can significantly improve VQE algorithms.
- [6] arXiv:2404.19032 [pdf, other]
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Title: Fermionic Machine LearningSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We introduce fermionic machine learning (FermiML), a machine learning framework based on fermionic quantum computation. FermiML models are expressed in terms of parameterized matchgate circuits, a restricted class of quantum circuits that map exactly to systems of free Majorana fermions. The FermiML framework allows for building fermionic counterparts of any quantum machine learning (QML) model based on parameterized quantum circuits, including models that produce highly entangled quantum states. Importantly, matchgate circuits are efficiently simulable classically, thus rendering FermiML a flexible framework for utility benchmarks of QML methods on large real-world datasets. We initiate the exploration of FermiML by benchmarking it against unrestricted PQCs in the context of classification with random quantum kernels. Through experiments on standard datasets (Digits and Wisconsin Breast Cancer), we demonstrate that FermiML kernels are on-par with unrestricted PQC kernels in classification tasks using support-vector machines. Furthermore, we find that FermiML kernels outperform their unrestricted candidates on multi-class classification, including on datasets with several tens of relevant features. We thus show how FermiML enables us to explore regimes previously inaccessible to QML methods.
- [7] arXiv:2404.19036 [pdf, other]
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Title: Non-resonant electric quantum control of individual on-surface spinsComments: 6 pages, 5 figuresSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Quantum control techniques play an important role in manipulating and harnessing the properties of different quantum systems, including isolated atoms. Here, we propose to achieve quantum control over a single on-surface atomic spin using Landau-Zener-St\"uckelberg-Majorana (LZSM) interferometry implemented with Scanning Tunneling Microscopy (STM). Specifically, we model how the application of time-dependent, non-resonant AC electric fields across the STM tip-surface gap makes it possible to achieve precise quantum state manipulation in an isolated Fe atom on a MgO/Ag(100) surface. We propose a protocol to combine Landau Zener tunneling with LZSM interferometry that permits one to measure the quantum spin tunneling of an individual Fe atom. The proposed experiments can be implemented with ESR-STM instrumentation, opening a new venue in the research of on-surface single spin control.
- [8] arXiv:2404.19047 [pdf, other]
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Title: Continuous feedback protocols for cooling and trapping a quantum harmonic oscillatorAuthors: Guilherme De Sousa, Pharnam Bakhshinezhad, Björn Annby-Andersson, Peter Samuelsson, Patrick P. Potts, Christopher JarzynskiComments: 18 pages, 3 figuresSubjects: Quantum Physics (quant-ph)
Quantum technologies and experiments often require preparing systems in low-temperature states. Here, we investigate cooling schemes using feedback protocols modeled with a Quantum Fokker-Planck Master Equation (QFPME) recently derived by Annby-Andersson et. al. (Phys. Rev. Lett. 129, 050401, 2022). This equation describes systems under continuous weak measurements, with feedback based on the outcome of these measurements. We apply this formalism to study the cooling and trapping of a harmonic oscillator for several protocols based on position and/or momentum measurements. We find that the protocols can cool the oscillator down to, or close to, the ground state for suitable choices of parameters. Our analysis provides an analytically solvable case study of quantum measurement and feedback and illustrates the application of the QFPME to continuous quantum systems.
- [9] arXiv:2404.19067 [pdf, other]
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Title: An Early Investigation of the HHL Quantum Linear Solver for Scientific ApplicationsAuthors: Muqing Zheng, Chenxu Liu, Samuel Stein, Xiangyu Li, Johannes Mülmenstädt, Yousu Chen, Ang LiComments: 21 pages, 8 figuresSubjects: Quantum Physics (quant-ph)
In this paper, we explore using the Harrow-Hassidim-Lloyd (HHL) algorithm to address scientific and engineering problems through quantum computing utilizing the NWQSim simulation package on high-performance computing. Focusing on domains such as power-grid management and heat transfer problems, we demonstrate the correlations of the precision of quantum phase estimation, along with various properties of coefficient matrices, on the final solution and quantum resource cost in iterative and non-iterative numerical methods such as Newton-Raphson method and finite difference method, as well as their impacts on quantum error correction costs using Microsoft Azure Quantum resource estimator. We conclude the exponential resource cost from quantum phase estimation before and after quantum error correction and illustrate a potential way to reduce the demands on physical qubits. This work lays down a preliminary step for future investigations, urging a closer examination of quantum algorithms' scalability and efficiency in domain applications.
- [10] arXiv:2404.19082 [pdf, other]
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Title: Stability of Quantum ComputersAuthors: Samudra DasguptaComments: PhD dissertationSubjects: Quantum Physics (quant-ph)
Quantum computing's potential is immense, promising super-polynomial reductions in execution time, energy use, and memory requirements compared to classical computers. This technology has the power to revolutionize scientific applications such as simulating many-body quantum systems for molecular structure understanding, factorization of large integers, enhance machine learning, and in the process, disrupt industries like telecommunications, material science, pharmaceuticals and artificial intelligence. However, quantum computing's potential is curtailed by noise, further complicated by non-stationary noise parameter distributions across time and qubits. This dissertation focuses on the persistent issue of noise in quantum computing, particularly non-stationarity of noise parameters in transmon processors.
- [11] arXiv:2404.19105 [pdf, other]
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Title: Optimal tradeoffs for estimating Pauli observablesComments: 59 pages, 1 figureSubjects: Quantum Physics (quant-ph); Information Theory (cs.IT)
We revisit the problem of Pauli shadow tomography: given copies of an unknown $n$-qubit quantum state $\rho$, estimate $\text{tr}(P\rho)$ for some set of Pauli operators $P$ to within additive error $\epsilon$. This has been a popular testbed for exploring the advantage of protocols with quantum memory over those without: with enough memory to measure two copies at a time, one can use Bell sampling to estimate $|\text{tr}(P\rho)|$ for all $P$ using $O(n/\epsilon^4)$ copies, but with $k\le n$ qubits of memory, $\Omega(2^{(n-k)/3})$ copies are needed.
These results leave open several natural questions. How does this picture change in the physically relevant setting where one only needs to estimate a certain subset of Paulis? What is the optimal dependence on $\epsilon$? What is the optimal tradeoff between quantum memory and sample complexity?
We answer all of these questions. For any subset $A$ of Paulis and any family of measurement strategies, we completely characterize the optimal sample complexity, up to $\log |A|$ factors. We show any protocol that makes $\text{poly}(n)$-copy measurements must make $\Omega(1/\epsilon^4)$ measurements. For any protocol that makes $\text{poly}(n)$-copy measurements and only has $k < n$ qubits of memory, we show that $\widetilde{\Theta}(\min\{2^n/\epsilon^2, 2^{n-k}/\epsilon^4\})$ copies are necessary and sufficient.
The protocols we propose can also estimate the actual values $\text{tr}(P\rho)$, rather than just their absolute values as in prior work. Additionally, as a byproduct of our techniques, we establish tight bounds for the task of purity testing and show that it exhibits an intriguing phase transition not present in the memory-sample tradeoff for Pauli shadow tomography. - [12] arXiv:2404.19140 [pdf, other]
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Title: Many-body quantum thermal machines in a Lieb-kagome Hubbard modelComments: Preliminary draft, comments welcomedSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
Quantum many-body systems serve as a suitable working medium for realizing quantum thermal machines (QTMs) by offering distinct advantages such as cooperative many-body effects, and performance boost at the quantum critical points. However, the bulk of the existing literature exploring the criticality of many-body systems in the context of QTMs involves models sans the electronic interactions, which are non-trivial to deal with and require sophisticated numerical techniques. Here we adopt the prototypical Hubbard model in two dimensions (2D) in the framework of the line graph Lieb-kagome lattice for the working medium of a multi-functional QTM. We resort to a non-perturbative, static path approximated (SPA) Monte Carlo technique to deal with the repulsive Hubbard model. We observe that in a Stirling cycle, in both the interacting and non-interacting limits, the heat engine function dominates and its performance gets better when the strain is induced from the kagome to the Lieb limit, while for the reverse the refrigeration action is preferred. Further, we show that the QTM performs better when the difference between the temperatures of the two baths is lower and the QTM reaches the Carnot limit in this regime. Further, we extensively study the performance of the QTM in the repulsive Hubbard interacting regime where the magnetic orders come into the picture. We explore the performance of the QTM along the quantum critical points and in the large interaction limit.
- [13] arXiv:2404.19199 [pdf, other]
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Title: Near-ultrastrong nonlinear light-matter coupling in superconducting circuitsAuthors: Yufeng Ye, Jeremy B. Kline, Alec Yen, Gregory Cunningham, Max Tan, Alicia Zang, Michael Gingras, Bethany M. Niedzielski, Hannah Stickler, Kyle Serniak, Mollie E. Schwartz, Kevin P. O'BrienSubjects: Quantum Physics (quant-ph)
The interaction between an atom and an electromagnetic mode of a resonator is of both fundamental interest and is ubiquitous in quantum technologies. Most prior work studies a linear light-matter coupling of the form $g \widehat{\sigma}_x (\widehat{a} + \widehat{a}^\dagger)$, where $g$ measured relative to photonic ($\omega_a$) and atomic ($\omega_b$) mode frequencies can reach the ultrastrong regime ($g/\omega_{a}\!>\!10^{-1}$). In contrast, a nonlinear light-matter coupling of the form $\frac{\chi}{2} \widehat{\sigma}_z \widehat{a}^\dagger \widehat{a}$ has the advantage of commuting with the atomic $\widehat{\sigma}_z$ and photonic $\widehat{a}^\dagger\widehat{a}$ Hamiltonian, allowing for fundamental operations such as quantum-non-demolition measurement. However, due to the perturbative nature of nonlinear coupling, the state-of-the-art $\chi/\text{max}(\omega_a, \omega_b)$ is limited to $\!<\!10^{-2}$. Here, we use a superconducting circuit architecture featuring a quarton coupler to experimentally demonstrate, for the first time, a near-ultrastrong $\chi/\text{max}(\omega_a, \omega_b)= (4.852\pm0.006)\times10^{-2}$ nonlinear coupling of a superconducting artificial atom and a nearly-linear resonator. We also show signatures of light-light nonlinear coupling ($\chi\widehat{a}^\dagger\widehat{a}\widehat{b}^\dagger\widehat{b}$), and $\chi/2\pi = 580.3 \pm 0.4 $ MHz matter-matter nonlinear coupling ($\frac{\chi}{4}\widehat{\sigma}_{z,a}\widehat{\sigma}_{z,b}$) which represents the largest reported $ZZ$ interaction between two coherent qubits. Such advances in the nonlinear coupling strength of light, matter modes enable new physical regimes and could lead to applications such as orders of magnitude faster qubit readout and gates.
- [14] arXiv:2404.19211 [pdf, other]
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Title: Triply efficient shadow tomographySubjects: Quantum Physics (quant-ph)
Given copies of a quantum state $\rho$, a shadow tomography protocol aims to learn all expectation values from a fixed set of observables, to within a given precision $\epsilon$. We say that a shadow tomography protocol is triply efficient if it is sample- and time-efficient, and only employs measurements that entangle a constant number of copies of $\rho$ at a time. The classical shadows protocol based on random single-copy measurements is triply efficient for the set of local Pauli observables. This and other protocols based on random single-copy Clifford measurements can be understood as arising from fractional colorings of a graph $G$ that encodes the commutation structure of the set of observables. Here we describe a framework for two-copy shadow tomography that uses an initial round of Bell measurements to reduce to a fractional coloring problem in an induced subgraph of $G$ with bounded clique number. This coloring problem can be addressed using techniques from graph theory known as chi-boundedness. Using this framework we give the first triply efficient shadow tomography scheme for the set of local fermionic observables, which arise in a broad class of interacting fermionic systems in physics and chemistry. We also give a triply efficient scheme for the set of all $n$-qubit Pauli observables. Our protocols for these tasks use two-copy measurements, which is necessary: sample-efficient schemes are provably impossible using only single-copy measurements. Finally, we give a shadow tomography protocol that compresses an $n$-qubit quantum state into a $\text{poly}(n)$-sized classical representation, from which one can extract the expected value of any of the $4^n$ Pauli observables in $\text{poly}(n)$ time, up to a small constant error.
- [15] arXiv:2404.19251 [pdf, other]
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Title: Quantum control in the presence of strongly coupled non-Markovian noiseSubjects: Quantum Physics (quant-ph); Systems and Control (eess.SY)
Controlling quantum systems under correlated non-Markovian noise, particularly when strongly coupled, poses significant challenges in the development of quantum technologies. Traditional quantum control strategies, heavily reliant on precise models, often fail under these conditions. Here, we address the problem by utilizing a data-driven graybox model, which integrates machine learning structures with physics-based elements. We demonstrate single-qubit control, implementing a universal gate set as well as a random gate set, achieving high fidelity under unknown, strongly-coupled non-Markovian non-Gaussian noise, significantly outperforming traditional methods. Our method is applicable to all open finite-dimensional quantum systems, regardless of the type of noise or the strength of the coupling.
- [16] arXiv:2404.19304 [pdf, other]
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Title: Boosting generation rate of squeezed single-photon states by generalized photon subtractionAuthors: Hiroko Tomoda, Akihiro Machinaga, Kan Takase, Jun Harada, Takahiro Kashiwazaki, Takeshi Umeki, Shigehito Miki, Fumihiro China, Masahiro Yabuno, Hirotaka Terai, Daichi Okuno, Shuntaro TakedaComments: 13 pages, 7 figuresSubjects: Quantum Physics (quant-ph)
In optical quantum information processing with continuous variables, optical non-Gaussian quantum states are essential for universal and fault-tolerant quantum computation. Experimentally, their most typical generation method is photon subtraction (PS) where single-photon detection by an on/off detector probabilistically heralds the generation of squeezed single-photon states. In PS, however, trying to avoid unwanted multi-photon detection inevitably limits the generation rate, hindering the application of squeezed single-photon states. Here, we theoretically show that generalized photon subtraction (GPS), a simple extension of PS, can improve the generation rate while maintaining the quality of the generated states. Furthermore, we experimentally demonstrate the generation rate improvement for 2 dB- and 4 dB-squeezed single-photon states compared to PS, by more than one order of magnitude particularly for the case of 2 dB. Our results will accelerate the application of squeezed single-photon states to more advanced quantum information protocols.
- [17] arXiv:2404.19308 [pdf, other]
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Title: A characterization of entangled two-qubit states via partial-transpose-momentsComments: 31 pages, LaTeX, 9 figuresJournal-ref: Annalen der Physik 534, 2200289 (2022)Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph); Optimization and Control (math.OC)
Although quantum entanglement is an important resource, its characterization is quite challenging. The partial transposition is a common method to detect bipartite entanglement. In this paper, the authors study the partial-transpose(PT)-moments of two-qubit states,and completely describe the whole region, composed of the second and third PT-moments, for all two-qubit states. Furthermore, they determine the accurate region corresponding to all entangled two-qubit states. The states corresponding to those boundary points of the whole region, and to the border lines between separable and entangled states are analyzed. As an application, they characterize the entangled region of PT-moments for the two families of Werner states and Bell-diagonal states. The relations between entanglement and the pairs of PT-moments are revealed from these typical examples. They also numerically plot the whole region of possible PT-moments for all two-qubit X-states, and find that this region is almost the same as the whole region of PT-moments for all two-qubit states. Moreover, they extend their results to detect the entanglement of multiqubit states. By utilizing the PT-moment-based method to characterize the entanglement of the multiqubit states mixed by the GHZ and W states, they propose an operational way of verifying the genuine entanglement in such states.
- [18] arXiv:2404.19312 [pdf, other]
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Title: Revealing the working mechanism of quantum neural networks by mutual informationSubjects: Quantum Physics (quant-ph)
Quantum neural networks (QNNs) is a parameterized quantum circuit model, which can be trained by gradient-based optimizer, can be used for supervised learning, regression tasks, combinatorial optimization, etc. Although many works have demonstrated that QNNs have better learnability, generalizability, etc. compared to classical neural networks. However, as with classical neural networks, we still can't explain their working mechanism well. In this paper, we reveal the training mechanism of QNNs by mutual information. Unlike traditional mutual information in neural networks, due to quantum computing remains information conserved, the mutual information is trivial of the input and output of U operator. In our work, in order to observe the change of mutual information during training, we divide the quantum circuit (U operator) into two subsystems, discard subsystem (D) and measurement subsystem (M) respectively. We calculate two mutual information, I(Di : Mo) and I(Mi : Mo) (i and o means input or output of the corresponding subsystem), and observe their behavior during training. As the epochs increases, I(Di : Mo) gradually increases, this may means some information of discard subsystem is continuously pushed into the measurement subsystem, the information should be label-related. What's more, I(Mi : Mo) exist two-phase behavior in training process, this consistent with the information bottleneck anticipation. The first phase, I(Mi : Mo) is increasing, this means the measurement subsystem perform feature fitting. The second phase, I(Mi : Mo) is decreasing, this may means the system is generalizing, the measurement subsystem discard label-irrelevant information into the discard subsystem as many as possible. Our work discussed the working mechanism of QNNs by mutual information, further, it can be used to analyze the accuracy and generalization of QNNs.
- [19] arXiv:2404.19313 [pdf, other]
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Title: High-precision chemical quantum sensing in flowing monodisperse microdropletsAuthors: Adrisha Sarkar, Zachary Jones, Madhur Parashar, Emanuel Druga, Amala Akkiraju, Sophie Conti, Pranav Krishnamoorthi, Srisai Nachuri, Parker Aman, Mohammad Hashemi, Nicholas Nunn, Marco Torelli, Benjamin Gilbert, Kevin R. Wilson, Olga Shenderova, Deepti Tanjore, Ashok AjoySubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph); Quantitative Methods (q-bio.QM)
We report on a novel flow-based method for high-precision chemical detection that integrates quantum sensing with droplet microfluidics. We deploy nanodiamond particles hosting fluorescent nitrogen vacancy defects as quantum sensors in flowing, monodisperse, picoliter-volume microdroplets containing analyte molecules. ND motion within these microcompartments facilitates close sensor-analyte interaction and mitigates particle heterogeneity. Microdroplet flow rates are rapid (upto 4cm/s) and with minimal drift. Pairing this controlled flow with microwave control of NV electronic spins, we introduce a new noise-suppressed mode of Optically Detected Magnetic Resonance that is sensitive to chemical analytes while resilient against experimental variations, achieving detection of analyte-induced signals at an unprecedented level of a few hundredths of a percent of the ND fluorescence. We demonstrate its application to detecting paramagnetic ions in droplets with simultaneously low limit-of-detection and low analyte volumes, in a manner significantly better than existing technologies. This is combined with exceptional measurement stability over >103s and across hundreds of thousands of droplets, while utilizing minimal sensor volumes and incurring low ND costs (<$0.70 for an hour of operation). Additionally, we demonstrate using these droplets as micro-confinement chambers by co-encapsulating ND quantum sensors with analytes, including single cells. This versatility suggests wide-ranging applications, like single-cell metabolomics and real-time intracellular measurements in bioreactors. Our work paves the way for portable, high-sensitivity, amplification-free, chemical assays with high throughput; introduces a new chemical imaging tool for probing chemical reactions in microenvironments; and establishes the foundation for developing movable, arrayed quantum sensors through droplet microfluidics.
- [20] arXiv:2404.19373 [pdf, other]
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Title: Entanglement Signature of the Superradiant Quantum Phase TransitionSubjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph); Optics (physics.optics)
Entanglement and quantum correlations between atoms are not usually considered key ingredients of the superradiant phase transition. Here we consider the Tavis-Cummings model, a solvable system of two-levels atoms, coupled with a single-mode quantized electromagnetic field. This system undergoes a superradiant phase transition, even in a finite-size framework, accompanied by a spontaneous symmetry breaking, and an infinite sequence of energy level crossings. We find approximated expressions for the ground state, its energy, and the position of the level crossings, valid in the limit of a very large number of photons with respect to that of the atoms. In that same limit, we find that the number of photons scales quadratically with the coupling strength, and linearly with the system size, providing a new insight into the superradiance phenomenon. Resorting to novel multipartite measures, we then demonstrate that this quantum phase transition is accompanied by a crossover in the quantum correlations and entanglement between the atoms (qubits). The latters therefore represent suited order parameters for this transition. Finally, we show that these properties of the quantum phase transition persist in the thermodynamic limit.
- [21] arXiv:2404.19386 [pdf, other]
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Title: Weighted Feedback-Based Quantum Algorithm for Excited States CalculationSubjects: Quantum Physics (quant-ph)
Drawing inspiration from the Lyapunov control technique for quantum systems, feedback-based quantum algorithms have been proposed for calculating the ground states of Hamiltonians. In this work, we consider extending these algorithms to tackle calculating excited states. Inspired by the weighted subspace-search variational quantum eigensolver algorithm, we propose a novel weighted feedback-based quantum algorithm for excited state calculation. We show that depending on how we design the weights and the feedback law, we can prepare the $p$th excited state or lowest energy states up to the $p$th excited state. Through an application in quantum chemistry, we show the effectiveness of the proposed algorithm, evaluating its efficacy via numerical simulations.
- [22] arXiv:2404.19408 [pdf, other]
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Title: A simple method for compiling quantum stabilizer circuitsAuthors: Brendan ReidComments: 9 pages, 4 figuresSubjects: Quantum Physics (quant-ph)
Stabilizer circuits play an important role in quantum error correction protocols, and will be vital for ensuring fault tolerance in future quantum hardware. While stabilizer circuits are defined on the Clifford generating set, {H, S, CX}, not all of these gates are native to quantum hardware. As such they must be compiled into the native gateset, with the key difference across hardware archetypes being the native two qubit gate. Here we introduce an intuitive and accessible method for Clifford gate compilation. While multiple open source solutions exist for quantum circuit compilation, these operate on arbitrary quantum gates. By restricting ourselves to Clifford gates, the compilation process becomes almost trivial and even large circuits can be compiled manually. The core idea is well known: if two Clifford circuits conjugate Paulis identically, they are equivalent. Compilation is then reduced to ensuring that the instantaneous Pauli conjugation is correct for each qubit at every timestep. This is Tableaux Manipulation, so called as we directly interrogate stabilizer tableaux to ensure correct Pauli conjugation. We provide a brief explanation of the process along with some worked examples to build intuition; we finally show some comparisons for compiling large circuits to open source software, and highlight that this method ensures a minimal number of quantum gates are employed.
- [23] arXiv:2404.19428 [pdf, ps, other]
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Title: From Quantum Mechanics to Quantum Software EngineeringComments: 8 pagesSubjects: Quantum Physics (quant-ph); Software Engineering (cs.SE)
Victor Hugo's timeless observation, "Nothing is more powerful than an idea whose time has come", resonates today as Quantum Computing, once only a dream of a physicist, stands at the threshold of reality with the potential to revolutionise the world. To comprehend the surge of attention it commands today, one must delve into the motivations that birthed and nurtured Quantum Computing. While the past of Quantum Computing provides insights into the present, the future could unfold through the lens of Quantum Software Engineering. Quantum Software Engineering, guided by its principles and methodologies investigates the most effective ways to interact with Quantum Computers to unlock their true potential and usher in a new era of possibilities. To gain insight into the present landscape and anticipate the trajectory of Quantum Computing and Quantum Software Engineering, this paper embarks on a journey through their evolution and outlines potential directions for future research.
- [24] arXiv:2404.19445 [pdf, other]
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Title: How decoherence affects the security of BB84 quantum key distribution protocolSubjects: Quantum Physics (quant-ph)
We present how the mechanisms of quantum Darwinism allow for the leakage of information in the standard BB84 quantum key distribution protocol, a paradigmatic prepare and measure quantum cryptography scenario.
We work within the decoherence theory framework and employ the model of measurements provided by quantum Darwinism. We investigate how much of the information about the results crucial for the cryptographic key to be kept secret is leaked during the quantum measurement process and subsequently how much of that information might be later obtained by an eavesdropper using a type of a so-called Van Eck side-channel wiretapping.
We also show how the security can be affected by different ways of organizing the surrounding environment into layers, e.g. rooms or other divisions affecting the spread of quantum information in the environment and its interaction, paving a venue to potential enhancements, and insight into proper engineering of shieldings for cryptographical devices. - [25] arXiv:2404.19458 [pdf, other]
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Title: Simple loss-tolerant protocol for GHZ-state distribution in a quantum networkComments: 16 pages, 16 figuresSubjects: Quantum Physics (quant-ph)
Distributed quantum entanglement plays a crucial role in realizing networks that connect quantum devices. However, sharing entanglement between distant nodes by means of photons is a challenging process primary due to unavoidable losses in the linking channels. In this paper, we propose a simple loss-tolerant protocol for the Greenberger-Horne-Zeilinger state distribution. We analyze the distribution rate under feasible experimental conditions and demonstrate the advantages of rate-loss scaling with respect to direct transmission. Our protocol does not use quantum repeaters and is achievable with current quantum optics technology. The result has direct application to tasks such as conference key agreement or distributed sensing. Moreover, it reduces the requirements for implementing distributed quantum error correction codes such as the surface code.
- [26] arXiv:2404.19474 [pdf, ps, other]
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Title: Quantum Relaxation for Solving Multiple Knapsack ProblemsComments: 8 pagesSubjects: Quantum Physics (quant-ph)
Combinatorial problems are a common challenge in business, requiring finding optimal solutions under specified constraints. While significant progress has been made with variational approaches such as QAOA, most problems addressed are unconstrained (such as Max-Cut). In this study, we investigate a hybrid quantum-classical method for constrained optimization problems, particularly those with knapsack constraints that occur frequently in financial and supply chain applications. Our proposed method relies firstly on relaxations to local quantum Hamiltonians, defined through commutative maps. Drawing inspiration from quantum random access code (QRAC) concepts, particularly Quantum Random Access Optimizer (QRAO), we explore QRAO's potential in solving large constrained optimization problems. We employ classical techniques like Linear Relaxation as a presolve mechanism to handle constraints and cope further with scalability. We compare our approach with QAOA and present the final results for a real-world procurement optimization problem: a significant sized multi-knapsack-constrained problem.
- [27] arXiv:2404.19476 [pdf, ps, other]
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Title: Global Phase Helps in Quantum Search: Yet Another Look at the Welded Tree ProblemAuthors: Aleksandrs BelovsComments: 14 pages, 6 figuresSubjects: Quantum Physics (quant-ph)
Up to now, relatively few exponential quantum speed-ups have been achieved. Out of them, the welded tree problem (Childs, Cleve, Deotto, Farhi, Gutmann, and Spielman'2003) is one of the unusual examples, as the exponential speed-up is attained by a quantum walk. In this paper, we give a very short proof of the optimal linear hitting time for this problem by a discrete-time quantum walk, which is based on a simple modification of the electric quantum walk framework. The same technique can be applied to other 1-dimensional hierarchical graphs, yielding results similar to (Balasubramanian, Li, and Harrow'2023).
- [28] arXiv:2404.19488 [pdf, other]
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Title: Theoretical investigation of the relations between quantum decoherence and weak-to-strong measurement transitionComments: 9 pages, 3 figuresSubjects: Quantum Physics (quant-ph)
This paper delves into the crucial aspects of pointer-induced quantum decoherence and the transition between von Neumann's projective strong measurement and Aharonov's weak measurement. Both phenomena significantly impact the dynamical understanding of quantum measurement processes. Specifically, we focus on the interplay between quantum decoherence and the transition from weak to strong measurement by deducing and comparing the quantum decoherence and weak-to-strong measurement transition factors within a general model and using the well-known Stern-Gerlach experiment as an illustrative example. Our findings reveal that both phenomena can be effectively characterized by a universal transition factor intricately linked to the coupling between the system and the measurement apparatus. The analysis presented can clarify the mechanism behind the relations of quantum decoherence to the weak measurement and weak-to-strong measurement transition.
- [29] arXiv:2404.19497 [pdf, other]
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Title: Light Cone Cancellation for Variational Quantum Eigensolver AnsatzAuthors: Xinjian Yan, Xinwei Lee, Ningyi Xie, Yoshiyuki Saito, Leo Kurosawa, Nobuyoshi Asai, Dongsheng Cai, HoongChuin LauSubjects: Quantum Physics (quant-ph)
Variational Quantum Algorithms (VQAs) represent a class of algorithms that utilize a hybrid approach, combining classical and quantum computing techniques. In this approach, classical computers serve as optimizers that update circuit parameters to find approximate solutions to complex problems. In this study, we apply a method known as Light Cone Cancellation (LCC) to optimize variational circuits, effectively reducing the required number of qubits and gates for circuit simulation. We then evaluate the performance of LCC one of the VQAs -- the Variational Quantum Eigensolver (VQE) -- to address the Max-Cut problem. Compared with the Quantum Approximate Optimization Algorithm (QAOA), VQE offers greater degrees of freedom at lower circuit depths. By applying LCC to VQE, we can shift the complexity of circuit simulation from the number of qubits to the number of edges in the graph, i.e., from exponential time to polynomial time. This enables us to solve large problems up to 50 vertices, without actually simulating the entire circuit. From our simulation in a 7-qubit and a 27-qubit noisy devices, we show that LCC yields higher approximation ratios than those cases without LCC, implying that the effect of noise is reduced when LCC is applied.
- [30] arXiv:2404.19511 [pdf, other]
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Title: Thermalization via three-wave mixingSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We discuss thermalization in a multimode quantum cavity under unitary evolution. According to general principles, an isolated system with quadratic couplings does not exhibit thermalization. However, we find that three-wave perturbation, typical for instance in superconducting Josephson systems, may lead to thermalization into a Bose-Einstein distribution of occupations of the modes. The temperature of this state is dictated by energy conservation in this closed system, and the thermal distribution is robust against weak disturbances. We discuss how our findings open up new avenues to experimentally probe fundamental assumptions of statistical physics in solid-state systems.
- [31] arXiv:2404.19539 [pdf, other]
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Title: Path integral spin dynamics for quantum paramagnetsComments: 10 pages, 8 figuresSubjects: Quantum Physics (quant-ph); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
A path integral method, combined with atomistic spin dynamics simulations, has been developed to calculate thermal quantum expectation values using a classical approach. In this study, we show how to treat Hamiltonians with non-linear terms, that are relevant for describing uniaxial anisotropies and mechanical constraints. These interactions can be expressed solely through quadratic terms of the spin operator along one axis, that can be identified with the quantisation axis.
- [32] arXiv:2404.19554 [pdf, other]
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Title: Entanglement-assisted phase estimation algorithm for calculating dynamical response functionsSubjects: Quantum Physics (quant-ph)
Dynamical response functions are fundamental quantities to describe the excited-state properties in quantum many-body systems. Quantum algorithms have been proposed to evaluate these quantities by means of quantum phase estimation (QPE), where the energy spectra are directly extracted from the QPE measurement outcomes in the frequency domain. Accurate estimation of excitation energies and transition probabilities with these QPE-based approaches is, however, challenging because of the problem of spectral leakage (or peak broadening) which is inherent in the QPE algorithm. To overcome this issue, in this work we consider an extension of the QPE-based approach adopting the optimal entangled input states, which is known to achieve the Heisenberg-limited scaling for the estimation precision. We demonstrate that with this method the peaks in the calculated energy spectra are more localized than those calculated by the original QPE-based approaches, suggesting the mitigation of the spectral leakage problem. By analyzing the probability distribution with the entangled phase estimation, we propose a simple scheme to better estimate both the transition energies and the corresponding transition probabilities of the peaks of interest in the spectra. The validity of our prescription is demonstrated by numerical simulations in various quantum many-body problems: the spectral function of a simple electron-plasmon model in condensed-matter physics, the dipole transitions of the H$_2$O molecule in quantum chemistry, and the electromagnetic transitions of the $^6$Li nucleus in nuclear physics.
- [33] arXiv:2404.19592 [pdf, other]
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Title: Programmable activation of quantum emitters in high-purity silicon with focused carbon ion beamsAuthors: M. Hollenbach, N. Klingner, P. Mazarov, W. Pilz, A. Nadzeyka, F. Mayer, N. V. Abrosimov, L. Bischoff, G. Hlawacek, M. Helm, G. V. AstakhovComments: 7 pages, 5 figuresSubjects: Quantum Physics (quant-ph); Applied Physics (physics.app-ph)
Carbon implantation at the nanoscale is highly desired for the engineering of defect-based qubits in a variety of materials, including silicon, diamond, SiC and hBN. However, the lack of focused carbon ion beams does not allow for the full disclosure of their potential for application in quantum technologies. Here, we develop and use a carbon source for focused ion beams for the simultaneous creation of two types of quantum emitters in silicon, the W and G centers. Furthermore, we apply a multi-step implantation protocol for the programmable activation of the G centers with sub-100- nm resolution. This approach provides a route for significant enhancement of the creation yield of single G centers in carbon-free silicon wafers. Our experimental demonstration is an important step towards nanoscale engineering of telecom quantum emitters in silicon of high crystalline quality and isotope purity.
- [34] arXiv:2404.19648 [pdf, other]
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Title: Exploring the hierarchy of quantum correlations under thermal effects in two gravitational cat statesSubjects: Quantum Physics (quant-ph)
In this article, we investigate the hierarchy of quantum correlations between two gravitational cats states (modeled by two qubits). We use concurrence to quantify the entanglement between the two gravitational cat states. Quantum steering is employed to measure the steerabilities. We consider geometric quantum discord to quantify quantum correlations beyond entanglement. We show that the concurrence persists even when steerability is lost under thermal effects. We also show that the temperature influences the degree of quantum correlations between the two gravitational cat states. Besides, when the energy difference between the ground state and the first excited level becomes significant, the states become separable.
- [35] arXiv:2404.19659 [pdf, other]
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Title: Regularization of Riemannian optimization: Application to process tomography and quantum machine learningSubjects: Quantum Physics (quant-ph)
Gradient descent algorithms on Riemannian manifolds have been used recently for the optimization of quantum channels. In this contribution, we investigate the influence of various regularization terms added to the cost function of these gradient descent approaches. Motivated by Lasso regularization, we apply penalties for large ranks of the quantum channel, favoring solutions that can be represented by as few Kraus operators as possible. We apply the method to quantum process tomography and a quantum machine learning problem. Suitably regularized models show faster convergence of the optimization as well as better fidelities in the case of process tomography. Applied to quantum classification scenarios, the regularization terms can simplify the classifying quantum channel without degrading the accuracy of the classification, thereby revealing the minimum channel rank needed for the given input data.
- [36] arXiv:2404.19679 [pdf, other]
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Title: Tuning the coherent interaction of an electron qubit and a nuclear magnonAuthors: Noah Shofer, Leon Zaporski, Martin Hayhurst Appel, Santanu Manna, Saimon Covre da Silva, Alexander Ghorbal, Urs Haeusler, Armando Rastelli, Claire Le Gall, Michał Gawełczyk, Mete Atatüre, Dorian A. GangloffComments: 9 pages, 5 figures, and Supplementary MaterialsSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A central spin qubit interacting coherently with an ensemble of proximal spins can be used to engineer entangled collective states or a multi-qubit register. Making full use of this many-body platform requires tuning the interaction between the central spin and its spin register. GaAs quantum dots offer a model realization of the central spin system where an electron qubit interacts with multiple ensembles of $\sim 10^{4}$ nuclear spins. In this work, we demonstrate tuning of the interaction between the electron qubit and the nuclear many-body system in a GaAs quantum dot. The homogeneity of the GaAs system allows us to perform high-precision and isotopically selective nuclear sideband spectroscopy, which reveals the single-nucleus electronic Knight field. Together with time-resolved spectroscopy of the nuclear field, this fully characterizes the electron-nuclear interaction for a priori control. An algorithmic feedback sequence selects the nuclear polarization precisely, which adjusts the electron-nuclear exchange interaction in situ via the electronic g-factor anisotropy. This allows us to tune directly the activation rate of a collective nuclear excitation (magnon) and the coherence time of the electron qubit. Our method is applicable to similar central-spin systems and enables the programmable tuning of coherent interactions in the many-body regime.
- [37] arXiv:2404.19680 [pdf, other]
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Title: Many-body quantum register for a spin qubitAuthors: Martin Hayhurst Appel, Alexander Ghorbal, Noah Shofer, Leon Zaporski, Santanu Manna, Saimon Filipe Covre da Silva, Urs Haeusler, Claire Le Gall, Armando Rastelli, Dorian A. Gangloff, Mete AtatüreSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Quantum networks require quantum nodes with coherent optical interfaces and multiple stationary qubits. In terms of optical properties, semiconductor quantum dots are highly compelling, but their adoption as quantum nodes has been impaired by the lack of auxiliary qubits. Here, we demonstrate a functional quantum register in a semiconductor quantum dot leveraging the dense, always-present nuclear spin ensemble. We prepare 13,000 host nuclear spins into a single many-body dark state to operate as the register logic state $|0\rangle$. The logic state $|1\rangle$ is defined as a single nuclear magnon excitation, enabling controlled quantum-state transfer between the electron spin qubit and the nuclear magnonic register. Using 130-ns SWAP gates, we implement a full write-store-retrieve-readout protocol with 68.6(4)% raw overall fidelity and a storage time of 130(16) $\mu$s in the absence of dynamical decoupling. Our work establishes how many-body physics can add step-change functionality to quantum devices, in this case transforming quantum dots into multi-qubit quantum nodes with deterministic registers.
- [38] arXiv:2404.19685 [pdf, other]
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Title: Enhanced twist-and-turn dynamics of spin squeezing in internal bosonic Josephson junctionsComments: 12 pages, 4 figuresSubjects: Quantum Physics (quant-ph)
The twist-and-turn dynamics of spin squeezing results from the interplay of the (nonlinear) one-axis-twisting- and the (linear) transverse-field turning term in the underlying Hamiltonian, both with constant (time-independent) respective coupling strengths. Using the methods of shortcuts to adiabaticity (STA) and their recently proposed enhanced version (eSTA), we demonstrate here that dynamics of this type can be utilized for a fast and robust preparation of spin-squeezed states in internal bosonic Josephson junctions -- condensates of cold bosonic atoms in two different internal (hyperfine) states (single-boson modes). Assuming that the initial state of this system is the coherent spin state with all the bosons in the equal superposition of the two single-boson modes and that the nonlinear-coupling strength in this system remains constant, we set out to determine the time-dependence of the linear-coupling strength using the STA and eSTA approaches. We then quantitatively characterize the modified twist-and-turn dynamics in this system by evaluating the coherent spin-squeezing- and number-squeezing parameters, as well as the fidelity of the target spin-squeezed states. In this manner, we show that the eSTA approach allows for a particularly robust experimental realization of strongly spin-squeezed states in this system, consistently outperforming its adiabatic and STA-based counterparts, even for systems with several hundred particles.
- [39] arXiv:2404.19712 [pdf, other]
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Title: QuTracer: Mitigating Quantum Gate and Measurement Errors by Tracing Subsets of QubitsSubjects: Quantum Physics (quant-ph)
Quantum error mitigation plays a crucial role in the current noisy-intermediate-scale-quantum (NISQ) era. As we advance towards achieving a practical quantum advantage in the near term, error mitigation emerges as an indispensable component. One notable prior work, Jigsaw, demonstrates that measurement crosstalk errors can be effectively mitigated by measuring subsets of qubits. Jigsaw operates by running multiple copies of the original circuit, each time measuring only a subset of qubits. The localized distributions yielded from measurement subsetting suffer from less crosstalk and are then used to update the global distribution, thereby achieving improved output fidelity. Inspired by the idea of measurement subsetting, we propose QuTracer, a framework designed to mitigate both gate and measurement errors in subsets of qubits by tracing the states of qubit subsets throughout the computational process. In order to achieve this goal, we introduce a technique, qubit subsetting Pauli checks (QSPC), which utilizes circuit cutting and Pauli Check Sandwiching (PCS) to trace the qubit subsets distribution to mitigate errors. The QuTracer framework can be applied to various algorithms including, but not limited to, VQE, QAOA, quantum arithmetic circuits, QPE, and Hamiltonian simulations. In our experiments, we perform both noisy simulations and real device experiments to demonstrate that QuTracer is scalable and significantly outperforms the state-of-the-art approaches.
- [40] arXiv:2404.19720 [pdf, other]
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Title: Efficient Multiparty Quantum Key Distribution over Quantum NetworksSubjects: Quantum Physics (quant-ph)
Multiparty quantum key distribution (QKD) is useful for many applications that involve secure communication or collaboration among multiple parties. While it can be achieved using pairwise QKD, a more efficient approach is to achieve it using multipartite entanglement distributed over quantum networks that connect the multiple parties. Existing studies on multipartite entanglement distribution, however, are not designed for multiparty QKD, and hence do not aim to maximize secret key generation rate. In this paper, we design efficient strategies for multiparty QKD over quantum networks. For 3-party QKD, we derive closed-form expressions for analyzing key distribution over quantum networks. We then use it to develop an efficient strategy for 3-party QKD by packing multiple stars that connect the 3 parties. For the general form of N-party QKD, we develop an approach that packs multiple trees to connect the N parties, while directly incorporating the estimated key rates on network paths. Extensive evaluation of our strategies, in both grid and random graphs, under a wide range of settings, demonstrates that our schemes achieve high key rate, which degrades gracefully when increasing the number of parties.
- [41] arXiv:2404.19727 [pdf, other]
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Title: Expressiveness of Commutative Quantum Circuits: A Probabilistic ApproachSubjects: Quantum Physics (quant-ph)
This study investigates the frame potential and expressiveness of commutative quantum circuits. Based on the Fourier series representation of these circuits, we express quantum expectation and pairwise fidelity as characteristic functions of random variables, and expressiveness as the recurrence probability of a random walk on a lattice. A central outcome of our work includes formulas to approximate the frame potential and expressiveness for any commutative quantum circuit, underpinned by convergence theorems in probability theory. We identify the lattice volume of the random walk as means to approximate expressiveness based on circuit architecture. In the specific case of commutative circuits involving Pauli-$Z$ rotations, we provide theoretical results relating expressiveness and circuit structure. Our probabilistic representation also provide means for bounding and approximately calculating the frame potential of a circuit through sampling methods.
- [42] arXiv:2404.19754 [pdf, other]
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Title: Succinct arguments for QMA from standard assumptions via compiled nonlocal gamesComments: 57 pagesSubjects: Quantum Physics (quant-ph); Cryptography and Security (cs.CR)
We construct a succinct classical argument system for QMA, the quantum analogue of NP, from generic and standard cryptographic assumptions. Previously, building on the prior work of Mahadev (FOCS '18), Bartusek et al. (CRYPTO '22) also constructed a succinct classical argument system for QMA. However, their construction relied on post-quantumly secure indistinguishability obfuscation, a very strong primitive which is not known from standard cryptographic assumptions. In contrast, the primitives we use (namely, collapsing hash functions and a mild version of quantum homomorphic encryption) are much weaker and are implied by standard assumptions such as LWE. Our protocol is constructed using a general transformation which was designed by Kalai et al. (STOC '23) as a candidate method to compile any quantum nonlocal game into an argument system. Our main technical contribution is to analyze the soundness of this transformation when it is applied to a succinct self-test for Pauli measurements on maximally entangled states, the latter of which is a key component in the proof of MIP*=RE in quantum complexity.
Cross-lists for Wed, 1 May 24
- [43] arXiv:2404.19004 (cross-list from cond-mat.str-el) [pdf, other]
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Title: Topological holography for fermionsComments: 44 pages, 19 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
Topological holography is a conjectured correspondence between the symmetry charges and defects of a $D$-dimensional system with the anyons in a $(D+1)$-dimensional topological order: the symmetry topological field theory (SymTFT). Topological holography is conjectured to capture the topological aspects of symmetry in gapped and gapless systems, with different phases corresponding to different gapped boundaries (anyon condensations) of the SymTFT. This correspondence was previously considered primarily for bosonic systems, excluding many phases of condensed matter systems involving fermionic electrons. In this work, we extend the SymTFT framework to establish a topological holography correspondence for fermionic systems. We demonstrate that this fermionic SymTFT framework captures the known properties of $1+1D$ fermion gapped phases and critical points, including the classification, edge-modes, and stacking rules of fermionic symmetry-protected topological phases (SPTs), and computation of partition functions of fermionic conformal field theories (CFTs). Beyond merely reproducing known properties, we show that the SymTFT approach can additionally serve as a practical tool for discovering new physics, and use this framework to construct a new example of a fermionic intrinsically gapless SPT phase characterized by an emergent fermionic anomaly.
- [44] arXiv:2404.19074 (cross-list from cond-mat.mes-hall) [pdf, other]
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Title: Chaos-Assisted Dynamical Tunneling in Flat Band SuperwiresComments: 12 pages, 6 FiguresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Recent theoretical investigations have revealed unconventional transport mechanisms within high Brilliouin zones of two-dimensional superlattices. Electrons can navigate along channels we call superwires, gently guided without brute force confinement. Such dynamical confinement is caused by weak superlattice deflections, markedly different from the static or energetic confinement observed in traditional wave guides or one-dimensional electron wires. The quantum properties of superwires give rise to elastic dynamical tunneling, linking disjoint regions of the corresponding classical phase space, and enabling the emergence of several parallel channels. This paper provides the underlying theory and mechanisms that facilitate dynamical tunneling assisted by chaos in periodic lattices. Moreover, we show that the mechanism of dynamical tunneling can be effectively conceptualized through the lens of a paraxial approximation. Our results further reveal that superwires predominantly exist within flat bands, emerging from eigenstates that represent linear combinations of conventional degenerate Bloch states. Finally, we quantify tunneling rates across various lattice configurations, and demonstrate the tunneling can be suppressed in a controlled fashion, illustrating potential implications in future nanodevices.
- [45] arXiv:2404.19102 (cross-list from astro-ph.GA) [pdf, other]
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Title: Modelling the Track of the GD-1 Stellar Stream Inside a Host with a Fermionic Dark Matter Core-Halo DistributionAuthors: Martín F. Mestre, Carlos R. Argüelles, Daniel D. Carpintero, Valentina Crespi, Andreas KrutComments: Accepted for publication in A&A, 111 pages, 8 figuresSubjects: Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
Traditional studies on stellar streams typically involve phenomenological $\Lambda$CDM halos or ad hoc dark matter (DM) profiles with different degrees of triaxiality, which preclude to gain insights into the nature and mass of the DM particles. Recently, a Maximum Entropy Principle of halo formation has been applied to provide a DM halo model which incorporates the fermionic (quantum) nature of the particles, while leading to DM profiles which depend on the fermion mass. Such profiles develop a more general dense core - diluted halo morphology able to explain the Galactic rotation curve, while the degenerate fermion core can mimic the central massive black hole (BH). We attempt to model the GD-1 stellar stream using a spherical core-halo DM distribution for the host, which, at the same time, explains the dynamics of the S-cluster stars through its degenerate fermion-core with no central BH. We used two optimization algorithms in order to fit both the initial conditions of the stream orbit and the fermionic model. The stream observables are 5D phase-space data from the Gaia DR2 survey. We were able to find good fits for both the GD-1 stream and the S-stars for a family of fermionic core-halo profiles parameterized by the fermion mass. This work provides evidence that the fermionic profile is a reliable model for both the massive central object and the DM of the Galaxy. Remarkably, this model predicts a total MW mass of $2.3\times 10^{11}M_{\odot}$ which is in agreement with recent mass estimates obtained from Gaia DR3 rotation curves (Gaia RC). In summary, with one single fermionic model for the DM distribution of the MW, we obtain a good fit in three totally different distance scales of the Galaxy: $\sim 10^{-6}$ kpc (central, S-stars), $\sim14$ kpc (mid, GD-1) and $\sim 30$ kpc (boundary, Gaia RC mass estimate).
- [46] arXiv:2404.19106 (cross-list from cond-mat.mes-hall) [pdf, other]
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Title: Bilayer graphene in periodic and quasiperiodic magnetic superlatticesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Starting from the effective Hamiltonian arising from the tight binding model, we study the behaviour of low-lying excitations for bilayer graphene placed in periodic external magnetic fields by using irreducible second order supersymmetry transformations. The coupled system of equations describing these excitations is reduced to a pair of periodic Schr\"odinger Hamiltonians intertwined by a second order differential operator. The direct implementation of more general second-order supersymmetry transformations allows to create nonsingular Schr\"odinger potentials with periodicity defects and bound states embedded in the forbidden bands, which turn out to be associated to quasiperiodic magnetic superlattices.
- [47] arXiv:2404.19142 (cross-list from physics.optics) [pdf, other]
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Title: Purcell enhanced optical refrigerationComments: 6 pagesSubjects: Optics (physics.optics); Quantum Physics (quant-ph)
Optical refrigeration of solids with anti-Stokes fluorescence has been widely explored as a vibration-free cryogenic cooling technology. A minimum temperature of 87 K has been demonstrated with rare-earth ion doped crystals using optical refrigeration. However, the depletion of the upper-lying energy levels in the ground state manifold hinders further cooling to below liquid nitrogen (LN$_2$) temperatures, confining its applications. In this work, we introduce a Purcell enhanced optical refrigeration method to circumvent this limitation. This approach enhances the emission of high energy photons by coupling to a nearby nanocavity, blue shifting the mean emission wavelength. Such Purcell enhanced emission facilitates cooling starting from a lower energy level in the ground state manifold, which exhibits a higher occupation below LN$_2$ temperatures. Using our experimentally measured optical coefficients, our theoretical analysis predicts a minimum achievable temperature of 38 K for a Yb$^{3+}$:YLiF$_{4}$ nanocrystal near a cavity under realistic conditions. The proposed method is applicable to other rare-earth ion doped materials and semiconductors, and will have applications in creating superconducting and other quantum devices with solid-state cooling.
- [48] arXiv:2404.19172 (cross-list from physics.chem-ph) [pdf, other]
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Title: Striking the Right Balance of Encoding Electron Correlation in the Hamiltonian and the Wavefunction AnsatzComments: 12 pages, 4 figures, 1 tableSubjects: Chemical Physics (physics.chem-ph); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
Multi-configurational electronic structure theory delivers the most versatile approximations to many-electron wavefunctions, flexible enough to deal with all sorts of transformations, ranging from electronic excitations, to open-shell molecules and chemical reactions. Multi-configurational models are therefore essential to establish universally applicable, predictive ab initio methods for chemistry. Here, we present a discussion of explicit correlation approaches which address the nagging problem of dealing with static and dynamic electron correlation in multi-configurational active-space approaches. We review the latest developments and then point to their key obstacles. Our discussion is supported by new data obtained with tensor network methods. We argue in favor of simple electrons-only correlator expressions that may allow one to define transcorrelated models in which the correlator does not bear a dependence on molecular structure.
- [49] arXiv:2404.19216 (cross-list from gr-qc) [pdf, other]
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Title: Optimal quantum strategy for locating Unruh channelsComments: 15 pages, 6 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
From the perspective of quantum information theory, the effect of Unruh radiation on a two-level accelerated detector can be modeled as a quantum channel. In this work, we employ the tools of channel-position finding to locate Unruh channels. The signal-idler and idler-free protocols are explored to determine the position of the target Unruh channel within a sequence of background channels. We derive the fidelity-based bounds for the ultimate error probability of each strategy and obtain the conditions where the signal-idler protocol is superior to the protocol involving idler-free states. It is found that the lower bound of the error probability for the signal-idler scheme exhibits clear advantages in all cases, while the idler-free scheme can only be implemented when the temperature of the two channels is very close and the number of initial states is insufficient. Interestingly, it is shown that the optimal detection protocol relies on the residual correlations shared between the emitted probe state and the retained idler modes.
- [50] arXiv:2404.19440 (cross-list from cond-mat.mtrl-sci) [pdf, other]
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Title: Negative transit time in non-tunneling electron transmission through graphene multilayersComments: 9 pages, 6 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph); Optics (physics.optics); Quantum Physics (quant-ph)
Attosecond dynamics of electron transmission through atomically-thin crystalline films is studied with an {\em ab initio} scattering theory. The temporal character of the electron propagation through graphene multilayers is traced to the band structure of bulk graphite: In the forbidden gaps the wave packet transit time $\tau_\mathrm{T}$ saturates with thickness and in the allowed bands $\tau_\mathrm{T}$ oscillates following transmission resonances. Hitherto unknown negative transit time due to in-plane scattering is discovered in monolayers of graphene, h-BN, and oxygen. Moreover, Wigner time delay is found to diverge at the scattering resonances caused by the emergence of secondary diffracted beams. This offers a way to manipulate the propagation timing of the wave packet without sacrificing the transmitted intensity. The spatial reshaping of the wave packet at the resonances may help elucidate details of the streaking by an inhomogeneous field at the surface.
- [51] arXiv:2404.19575 (cross-list from math.CA) [pdf, ps, other]
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Title: On the non-existence of oscillation numbers in Sturm-Liouville theoryAuthors: Angelo B. MingarelliComments: 21pages. To appear in Rocky Mountain J. MathSubjects: Classical Analysis and ODEs (math.CA); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We prove an old conjecture that relates the existence of non-real eigenvalues of Sturm-Liouville Dirichlet problems on a finite interval to the non-existence of oscillation numbers of its real eigenfunctions, [[6], p.104, Problems 3 and 5]. This extends to the general case, a previous result in [1], [2] where it was shown that the presence of even one pair of non-real eigenvalues implies the non-existence of a positive eigenfunction (or ground state). We also provide estimates on the Haupt and Richardson indices and Haupt and Richardson numbers thereby complementing the original Sturm oscillation theorem with the Haupt-Richardson oscillation theorem discovered over 100 years ago with estimates on the missing oscillation numbers of the real eigenfunctions observed.
- [52] arXiv:2404.19588 (cross-list from cond-mat.str-el) [pdf, other]
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Title: Boundary effect and quantum phases in spin chainsComments: 9 pages, 3 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Boundary effect is a widespread idea in many-body theories. However, it is more of a conceptual notion than a rigorously defined physical quantity. One can quantify the boundary effect by comparing two ground states of the same physical model, which differ only slightly in system size. Here, we analyze the quantity, which we call a boundary effect function, for an XXZ spin-1/2 model using density matrix renormalization group calculations. We find that three quantum phases of the model manifest as different functional forms of the boundary effect function. As a result, the quantum phase transition of the model is associated with a nonanalytic change of the boundary effect function. This work thus provides and concretizes a novel perspective on the relationship between bulk and boundary properties of ground states.
Replacements for Wed, 1 May 24
- [53] arXiv:2102.04394 (replaced) [pdf, other]
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Title: Learning with Density Matrices and Random FeaturesComments: Final version published in Quantum Mach. Intell. 4, 23 (2022)Journal-ref: Quantum Mach. Intell. 4, 23 (2022)Subjects: Machine Learning (cs.LG); Artificial Intelligence (cs.AI); Quantum Physics (quant-ph)
- [54] arXiv:2203.02886 (replaced) [pdf, other]
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Title: Strong DeterminismAuthors: Eddy Keming ChenComments: Accepted version, Philosophers' ImprintSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); History and Philosophy of Physics (physics.hist-ph)
- [55] arXiv:2212.12506 (replaced) [pdf, ps, other]
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Title: A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dotAuthors: Michele B. Rota, Tobias M. Krieger, Quirin Buchinger, Mattia Beccaceci, Julia Neuwirth, Hêlio Huet, Nikola Horová, Gabriele Lovicu, Giuseppe Ronco, Saimon F. Covre da Silva, Giorgio Pettinari, Magdalena Moczała-Dusanowska, Christoph Kohlberger, Santanu Manna, Sandra Stroj, Julia Freund, Xueyong Yuan, Christian Schneider, Miroslav Ježek, Sven Höfling, Francesco Basso Basset, Tobias Huber-Loyola, Armando Rastelli, Rinaldo TrottaSubjects: Quantum Physics (quant-ph); Materials Science (cond-mat.mtrl-sci)
- [56] arXiv:2303.07977 (replaced) [pdf, ps, other]
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Title: Direct generation of time-energy-entangled W triphotons in atomic vaporAuthors: Kangkang Li, Jianming Wen, Yin Cai, Saeid Vashahri Ghamsari, Changbiao Li, Feng Li, Zhaoyang Zhang, Yanpeng Zhang, Min XiaoComments: updated versionSubjects: Quantum Physics (quant-ph); Optics (physics.optics)
- [57] arXiv:2304.09480 (replaced) [pdf, other]
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Title: A revisit on the hydrogen atom induced by a uniform static electric fieldComments: 12 pages 3 figuresSubjects: Quantum Physics (quant-ph)
- [58] arXiv:2305.04704 (replaced) [pdf, other]
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Title: Operational Markovianization in Randomized BenchmarkingComments: 12+19 pages, 10 figuresJournal-ref: Quantum Sci. Technol. 9 035020 (2024)Subjects: Quantum Physics (quant-ph)
- [59] arXiv:2305.18204 (replaced) [pdf, other]
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Title: Kernel Density Matrices for Probabilistic Deep LearningSubjects: Machine Learning (cs.LG); Quantum Physics (quant-ph); Machine Learning (stat.ML)
- [60] arXiv:2306.05625 (replaced) [pdf, other]
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Title: Kerr-effect-based quantum logical gates in decoherence-free subspaceComments: 15 pages, 16 figuresSubjects: Quantum Physics (quant-ph)
- [61] arXiv:2307.10729 (replaced) [pdf, other]
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Title: Robust sparse IQP sampling in constant depthSubjects: Quantum Physics (quant-ph)
- [62] arXiv:2307.16737 (replaced) [pdf, other]
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Title: Nonstandard Hubbard model and electron pairingComments: 21 pages, 9 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
- [63] arXiv:2308.00601 (replaced) [pdf, other]
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Title: On Simultaneous Symplectic Diagonalization in the sense of Williamson's TheoremAuthors: Rudra KamatComments: 29 pagesSubjects: Rings and Algebras (math.RA); Mathematical Physics (math-ph); Symplectic Geometry (math.SG); Quantum Physics (quant-ph)
- [64] arXiv:2308.00753 (replaced) [pdf, other]
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Title: Bounding the joint numerical range of Pauli strings by graph parametersComments: 14+3 pages, 5 figuresSubjects: Quantum Physics (quant-ph)
- [65] arXiv:2308.07042 (replaced) [pdf, other]
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Title: Tensor network decompositions for absolutely maximally entangled statesComments: 21 pages, v2: a new Section in the Appendix, and some minor modificationsSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
- [66] arXiv:2308.15432 (replaced) [pdf, other]
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Title: Quantum Algorithm for Computing Distances Between SubspacesAuthors: Nhat A. NghiemSubjects: Quantum Physics (quant-ph)
- [67] arXiv:2308.15542 (replaced) [pdf, other]
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Title: Inelastic decay from integrabilityComments: Close to published versionJournal-ref: PRX Quantum 5, 020323 (2024)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
- [68] arXiv:2310.07054 (replaced) [pdf, other]
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Title: Simplifying the simulation of local Hamiltonian dynamicsComments: 13 pages, 6 figures, accepted version for publicationSubjects: Quantum Physics (quant-ph)
- [69] arXiv:2310.07568 (replaced) [pdf, other]
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Title: Angular Momentum Flows without anything carrying itComments: V3: 8 Pages, 2 Figures, improved description of approximationsSubjects: Quantum Physics (quant-ph)
- [70] arXiv:2311.08899 (replaced) [pdf, other]
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Title: Self-Organized Time Crystal in Driven-Dissipative Quantum SystemComments: 6 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Adaptation and Self-Organizing Systems (nlin.AO); Atomic Physics (physics.atom-ph)
- [71] arXiv:2311.10292 (replaced) [pdf, other]
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Title: Realization of a programmable multi-purpose photonic quantum memory with over-thousand qubit manipulationsComments: 17 pages, 19 figuresJournal-ref: Phys. Rev. X 14, 021018 (2024)Subjects: Quantum Physics (quant-ph); Emerging Technologies (cs.ET); Optics (physics.optics)
- [72] arXiv:2312.04221 (replaced) [pdf, ps, other]
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Title: Optimal quantum key distribution networks: capacitance versus securityComments: 12 pages, 6 figuresJournal-ref: npj Quantum Inf 10, 44 (2024)Subjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
- [73] arXiv:2401.15402 (replaced) [pdf, other]
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Title: Universality for Three Bosons with Large, Negative Effective Range: Aspects and AddendaAuthors: Harald W. Griesshammer (George Washington U.)Comments: 10 pages LaTeX2e (pdflatex) including 6 figures as 7 .pdf files using includegraphics and sn-jnl class. Contribution to the Proceedings of the 25th European Conference of Few-Body Physics, Mainz, 30 July - 4 August 2023. Typographical updates onlySubjects: Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Atomic and Molecular Clusters (physics.atm-clus); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
- [74] arXiv:2402.05756 (replaced) [pdf, other]
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Title: Non-Markovian Quantum Mpemba effectComments: v2, 4 pages, 3 figures and supplemental material. Substantially updated from v1Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
- [75] arXiv:2403.13505 (replaced) [pdf, ps, other]
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Title: Towards an All-Silicon QKD Transmitter Sourced by a Ge-on-Si Light EmitterAuthors: Florian Honz (1), Nemanja Vokić (1), Michael Hentschel (1), Philip Walther (2), Hannes Hübel (1), Bernhard Schrenk (1) ((1) AIT Austrian Institute of Technology, (2) University of Vienna, Faculty of Physics)Subjects: Quantum Physics (quant-ph)
- [76] arXiv:2404.17879 (replaced) [pdf, other]
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Title: Trapping polar molecules by surface acoustic wavesSubjects: Quantum Physics (quant-ph); Atomic and Molecular Clusters (physics.atm-clus)
- [77] arXiv:2404.18578 (replaced) [pdf, other]
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Title: Scheme for braiding Majorana zero modes in vortices using an STT-matrixSubjects: Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
- [78] arXiv:2404.18637 (replaced) [pdf, other]
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Title: QOSST: A Highly-Modular Open Source Platform for Experimental Continuous-Variable Quantum Key DistributionAuthors: Yoann Piétri, Matteo Schiavon, Valentina Marulanda Acosta, Baptiste Gouraud, Luis Trigo Vidarte, Philippe Grangier, Amine Rhouni, Eleni DiamantiComments: 15 pages, 8 figures; Corrected names in metadata and fileSubjects: Quantum Physics (quant-ph)
- [79] arXiv:2404.18777 (replaced) [pdf, other]
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Title: Quantum key distribution with displaced thermal statesComments: 18 pages, 10 figuresSubjects: Quantum Physics (quant-ph)
- [80] arXiv:2404.18828 (replaced) [pdf, other]
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Title: Demonstration of system-bath physics on gate-based quantum computerAuthors: Pascal Stadler, Matteo Lodi, Andisheh Khedri, Rolando Reiner, Kirsten Bark, Nicolas Vogt, Michael Marthaler, Juha LeppäkangasComments: 17 pages, 12 figures in total: 9 pages main text with 6 figuresSubjects: Quantum Physics (quant-ph)
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