IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-21 DOI: 10.22331/q-2026-04-21-2076

Iria W. Wang, Robin Brown, Taylor L. Patti, Anima Anandkumar, Marco Pavone, Susanne F. Yelin

{"title":"Elevating Variational Quantum Semidefinite Programs for Polynomial Objectives","authors":"Iria W. Wang, Robin Brown, Taylor L. Patti, Anima Anandkumar, Marco Pavone, Susanne F. Yelin","doi":"10.22331/q-2026-04-21-2076","DOIUrl":"https://doi.org/10.22331/q-2026-04-21-2076","url":null,"abstract":"Many practically important NP-hard optimization problems are inherently higher-order polynomial optimizations, which are typically addressed using approximation algorithms. Classical relaxations express polynomial objectives over a polynomial basis and solve the resulting quadratic objective as a semidefinite program, which can significantly inflate problem size and degrade approximation behavior. Variational quantum analogues to classical semidefinite programs (vQSDPs) are near-term formulations geared towards quadratic objectives. We introduce Product-State Lifting (PSL), a simple product-register encoding that upgrades any vQSDP with basis-state encoding to tackle $k$-degree polynomial optimization. This upgrade requires only a linear increase in resources with constraints constant in $k$. As a worked example, we pair PSL with the recently-proposed vQSDP with the Hadamard test and approximate amplitude constraints [Quantum 7, 1057 (2023)], and outline an application to Max-$k$SAT. PSL maintains the device-friendly structure of vQSDPs while making polynomial degree a linear resource parameter, offering a general path from quadratic to polynomial optimization without the constraint growth typical of classical relaxations.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"28 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147726624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Resource-theoretic hierarchy of contextuality for general probabilistic theories 一般概率理论的资源理论语境层次

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-21 DOI: 10.22331/q-2026-04-21-2077

Lorenzo Catani, Thomas D. Galley, Tomáš Gonda

{"title":"Resource-theoretic hierarchy of contextuality for general probabilistic theories","authors":"Lorenzo Catani, Thomas D. Galley, Tomáš Gonda","doi":"10.22331/q-2026-04-21-2077","DOIUrl":"https://doi.org/10.22331/q-2026-04-21-2077","url":null,"abstract":"In this work we present a hierarchy of generalized contextuality. It refines the traditional binary distinction between contextual and noncontextual theories, and facilitates their comparison based on how contextual they are. Our approach focuses on the contextuality of prepare-and-measure scenarios, described by general probabilistic theories (GPTs). To motivate the hierarchy, we define it as the resource ordering of a novel resource theory of GPT-contextuality. The building blocks of its free operations are classical systems and univalent simulations between GPTs. These simulations preserve operational equivalences and thus cannot generate contextuality. Noncontextual theories can be recovered as least elements in the hierarchy. We then define a new contextuality monotone, called classical excess, given by the minimal error of embedding a GPT within an infinite classical system. In addition, we show that the optimal success probability in the parity oblivious multiplexing game also defines a monotone in our resource theory. Finally, we discuss whether the non-free operations can be understood as implementing information erasure and thus explaining the fine-tuning aspect of contextuality.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"18 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147726840","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Comparing the performance of practical two-qubit gates for individual $^{171}$Yb ions in yttrium orthovanadate 正钒酸钇中单个Yb离子的实际双量子位门的性能比较

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-21 DOI: 10.22331/q-2026-04-21-2075

Mahsa Karimi, Faezeh Kimiaee Asadi, Stephen C. Wein, Christoph Simon

{"title":"Comparing the performance of practical two-qubit gates for individual $^{171}$Yb ions in yttrium orthovanadate","authors":"Mahsa Karimi, Faezeh Kimiaee Asadi, Stephen C. Wein, Christoph Simon","doi":"10.22331/q-2026-04-21-2075","DOIUrl":"https://doi.org/10.22331/q-2026-04-21-2075","url":null,"abstract":"In this paper, we investigate three schemes for implementing Controlled-Z (CZ) gates between individual ytterbium (Yb) rare-earth ions doped into yttrium orthovanadate (YVO$_4$ or YVO). Specifically, we investigate the CZ gates based on magnetic dipolar interactions between Yb ions, photon scattering off a cavity, and a photon interference-based protocol, with and without an optical cavity. We introduce a theoretical framework for precise computations of state and gate infidelities, accounting for noise effects. We then compute the state fidelity for each scheme to evaluate the feasibility of their experimental implementation. Based on these results, we compare the performance of the two-qubit gate schemes and discuss their respective advantages and disadvantages. We conclude that the probabilistic photon interference-based scheme offers the best fidelity scaling with cooperativity and is superior with the current technology of Yb values, while photon scattering is nearly deterministic but slower with less favourable fidelity scaling as a function of cooperativity. The cavityless magnetic dipolar scheme provides a fast, deterministic gate with decent fidelities if close ion localization can be realized. While focusing on $^{171}$Yb$^{3+}$:YVO system as a case study, the theoretical tools and approaches developed in this work are broadly applicable to other spin qubit systems.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"24 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147726839","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Estimating the best separable approximation of non-pure spin-squeezed states 估计非纯自旋压缩态的最佳可分离近似

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-21 DOI: 10.22331/q-2026-04-21-2078

Julia Mathé, Ayaka Usui, Otfried Gühne, Giuseppe Vitagliano

{"title":"Estimating the best separable approximation of non-pure spin-squeezed states","authors":"Julia Mathé, Ayaka Usui, Otfried Gühne, Giuseppe Vitagliano","doi":"10.22331/q-2026-04-21-2078","DOIUrl":"https://doi.org/10.22331/q-2026-04-21-2078","url":null,"abstract":"We discuss the estimation of the distance of a given mixed many-body quantum state to the set of fully separable states, applied to the concrete scenario of collective spin states. Concretely, we discuss lower bounds to distances from the set of fully separable states based on entanglement criteria and upper bounds to those distances using an iterative algorithm to find the optimal separable state closest to the target. Focusing on collective states of $N$ spin-$1/2$ particles, we consider spin-squeezing inequalities (SSIs), which provide a complete set of nonlinear entanglement criteria based on collective spin variances. First, we find a lower bound to distance-based entanglement monotones, specifically the so-called best separable approximation (BSA) from the complete set of SSIs, thereby bypassing entirely a numerical optimization over a (potentially very large) set of linear entanglement witnesses. Then, we improve current algorithms to iteratively find the closest separable state to a given target state, exploiting the symmetry of the system. These results allow us to study entanglement quantitatively on thermal states of spin systems on fully-connected graphs at nonzero temperature, as well as potentially similar states arising in out-of-equilibrium situations. We thus apply our methods to investigate entanglement across different phases of a fully-connected XXZ model. We observe that our lower bound becomes often tight for zero temperature as well as for the temperature at which entanglement disappears, both of which are thus precisely captured by the SSIs. We further observe, among other things, that entanglement can arise at nonzero temperature even in the ordered phase, where the ground state is separable, revealing the potential usefulness of entanglement quantification also beyond the ground state paradigm.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"12 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147726841","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

State preparation with parallel-sequential circuits 用并行顺序电路进行状态准备

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-21 DOI: 10.22331/q-2026-04-21-2079

Zhi-Yuan Wei, Daniel Malz

引用次数: 0

Quantum recurrences and the arithmetic of Floquet dynamics 量子递归与Floquet动力学算法

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-20 DOI: 10.22331/q-2026-04-20-2074

Amit Anand, Dinesh Valluri, Jack Davis, Shohini Ghose

{"title":"Quantum recurrences and the arithmetic of Floquet dynamics","authors":"Amit Anand, Dinesh Valluri, Jack Davis, Shohini Ghose","doi":"10.22331/q-2026-04-20-2074","DOIUrl":"https://doi.org/10.22331/q-2026-04-20-2074","url":null,"abstract":"The Poincaré recurrence theorem shows that conservative systems in a bounded region of phase space eventually return arbitrarily close to their initial state after a finite amount of time. An analogous behavior occurs in certain quantum systems where quantum states can recur after sufficiently long unitary evolution, a phenomenon known as quantum recurrence. Periodically driven (i.e. Floquet) quantum systems in particular exhibit complex dynamics even in small dimensions, motivating the study of how interactions and Hamiltonian structure affect recurrence behavior. While most studies treat recurrence in an approximate, distance-based sense, here we address the problem of {exact}, state-independent recurrences in a broad class of finite-dimensional Floquet systems, spanning both integrable and non-integrable models. Leveraging techniques from algebraic field theory, we construct an arithmetic framework that identifies all possible recurrence times by analyzing the cyclotomic structure of the Floquet unitary's spectrum. This computationally tractable approach yields both positive results, enumerating all candidate recurrence times, and definitive negative results, rigorously ruling out candidate recurrence times for a given set of Hamiltonian parameters. We further prove that rational Hamiltonian parameters do not, in general, guarantee exact recurrences, revealing a subtle interplay between system parameters and long-time dynamics. Our findings sharpen the theoretical understanding of quantum recurrences, clarify their relationship to quantum chaos, and highlight parameter regimes of special interest for quantum metrology and control.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"1 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147719744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Quantum convolutional channels and multiparameter families of 2-unitary matrices 量子卷积信道和2酉矩阵的多参数族

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-16 DOI: 10.22331/q-2026-04-16-2072

Rafał Bistroń, Jakub Czartowski, Karol Życzkowski

引用次数: 0

Quantum stick-slip motion in nanoscaled friction 纳米级摩擦中的量子粘滑运动

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-16 DOI: 10.22331/q-2026-04-16-2070

Dai-Nam Le, Pablo Rodriguez-Lopez, Lilia M. Woods

引用次数: 0

Diversity Methods for Improving Convergence and Accuracy of Quantum Error Correction Decoders Through Hardware Emulation 通过硬件仿真提高量子纠错译码器收敛和精度的分集方法

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-16 DOI: 10.22331/q-2026-04-16-2071

Francisco Garcia-Herrero, Javier Valls, Llanos Vergara-Picazo, Vicente Torres

{"title":"Diversity Methods for Improving Convergence and Accuracy of Quantum Error Correction Decoders Through Hardware Emulation","authors":"Francisco Garcia-Herrero, Javier Valls, Llanos Vergara-Picazo, Vicente Torres","doi":"10.22331/q-2026-04-16-2071","DOIUrl":"https://doi.org/10.22331/q-2026-04-16-2071","url":null,"abstract":"As quantum computing moves toward fault-tolerant architectures, quantum error correction (QEC) decoder performance is increasingly critical for scalability. Understanding the impact of transitioning from floating-point software to finite-precision hardware is essential, as hardware decoder performance affects code distance, qubit requirements, and connectivity between quantum and classical control units. This paper introduces a hardware emulator to evaluate QEC decoders using real hardware instead of software models. The emulator can explore $10^{13}$ different error patterns in 20 days with a single FPGA device running at 150 MHz, guaranteeing the decoder's performance at logical rates of $10^{-12}$, the requirement for most quantum algorithms. In contrast, an optimized C++ software on an Intel Core i9 with 128 GB RAM would take over a year to achieve similar results. The emulator also enables the storage of uncorrectable error patterns that generate logical errors, allowing for offline analysis and the design of new decoders. Using results from the emulator, we propose a method that combines several belief propagation (BP) decoders with different quantization levels, which we define as a diversity-based decoder. Individually, these decoders may show subpar error correction, but together they outperform the floating-point version of BP for quantum low-density parity-check (QLDPC) codes like hypergraph or lifted product. Preliminary results with circuit-level noise and bivariate bicycle codes suggest that hardware insights can also improve software. Our diversity-based proposal achieves a similar logical error rate as the well-known approach, BP with ordered statistics (BP+OSD) decoding, with average speed improvements ranging from 30% to 80%, and 10% to 120% in worst-case scenarios, while reducing post-processing algorithm activation from 47% to 96.93%, maintaining the same accuracy.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"60 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147695670","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Clifford-Deformed Compass Codes 克利福德-变形罗盘代码

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2026-04-16 DOI: 10.22331/q-2026-04-16-2073

Julie A. Campos, Kenneth R. Brown

引用次数: 0

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