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StoqMA vs. MA: the power of error reduction StoqMA vs. MA：减少误差的能力

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-11 DOI: 10.22331/q-2025-09-11-1853

Dorit Aharonov, Alex B. Grilo, Yupan Liu

引用次数: 0

Bayesian Quantum Amplitude Estimation 贝叶斯量子振幅估计

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-11 DOI: 10.22331/q-2025-09-11-1856

Alexandra Ramôa, Luis Paulo Santos

引用次数: 0

Expanding Hardware-Efficiently Manipulable Hilbert Space via Hamiltonian Embedding 利用哈密顿嵌入扩展硬件高效可操作希尔伯特空间

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-11 DOI: 10.22331/q-2025-09-11-1857

Jiaqi Leng, Joseph Li, Yuxiang Peng, Xiaodi Wu

{"title":"Expanding Hardware-Efficiently Manipulable Hilbert Space via Hamiltonian Embedding","authors":"Jiaqi Leng, Joseph Li, Yuxiang Peng, Xiaodi Wu","doi":"10.22331/q-2025-09-11-1857","DOIUrl":"https://doi.org/10.22331/q-2025-09-11-1857","url":null,"abstract":"Many promising quantum applications depend on the efficient quantum simulation of an exponentially large sparse Hamiltonian, a task known as sparse Hamiltonian simulation, which is fundamentally important in quantum computation. Although several theoretically appealing quantum algorithms have been proposed for this task, they typically require a black-box query model of the sparse Hamiltonian, rendering them impractical for near-term implementation on quantum devices.<br/> In this paper, we propose a technique named $textit{Hamiltonian embedding}$. This technique simulates a desired sparse Hamiltonian by embedding it into the evolution of a larger and more structured quantum system, allowing for more efficient simulation through hardware-efficient operations. We conduct a systematic study of this new technique and demonstrate significant savings in computational resources for implementing prominent quantum applications. As a result, we can now experimentally realize quantum walks on complicated graphs (e.g., binary trees, glued-tree graphs), quantum spatial search, and the simulation of real-space Schrödinger equations on current trapped-ion and neutral-atom platforms. Given the fundamental role of Hamiltonian evolution in the design of quantum algorithms, our technique markedly expands the horizon of implementable quantum advantages in the NISQ era.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"53 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145031858","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

Systematic construction of stabilizer codes via gauging abelian boundary symmetries 通过测量阿贝尔边界对称系统构造稳定器代码

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-08 DOI: 10.22331/q-2025-09-08-1852

Bram Vancraeynest-De Cuiper, José Garre-Rubio

{"title":"Systematic construction of stabilizer codes via gauging abelian boundary symmetries","authors":"Bram Vancraeynest-De Cuiper, José Garre-Rubio","doi":"10.22331/q-2025-09-08-1852","DOIUrl":"https://doi.org/10.22331/q-2025-09-08-1852","url":null,"abstract":"We propose a systematic framework to construct a $(d+1)$-dimensional stabilizer model from an initial generic d-dimensional abelian symmetry. Our approach builds upon the iterative gauging procedure, developed by one of the authors in [J. Garre-Rubio, Nature Commun. 15, 7986 (2024)][12], in which an initial symmetric state is repeatedly gauged to obtain an emergent model in one dimension higher that supports the initial symmetry at its boundary. This method not only enables the construction of emergent states and corresponding commuting stabilizer Hamiltonians of which they are ground states, but it also provides a way to construct gapped boundary conditions for these models that amount to spontaneously breaking part of the boundary symmetry. In a detailed introductory example, we showcase our paradigm by constructing three-dimensional Clifford-deformed surface codes from iteratively gauging a global 0-form symmetry that lives in two dimensions. We then provide a proof of our main result, hereby drawing upon a slight extension of the gauging procedure of Williamson. We additionally provide two more examples in $d=2$ in which different type-I fracton orders emerge from gauging initial linear subsystem and Sierpinski fractal symmetries. En passant, we provide explicit tensor network representations of all of the involved gauging maps and the emergent states.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"34 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145009470","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

Fault-tolerant hyperbolic Floquet quantum error correcting codes 容错双曲Floquet量子纠错码

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-05 DOI: 10.22331/q-2025-09-05-1849

Ali Fahimniya, Hossein Dehghani, Kishor Bharti, Sheryl Mathew, Alicia J. Kollár, Alexey V. Gorshkov, Michael J. Gullans

{"title":"Fault-tolerant hyperbolic Floquet quantum error correcting codes","authors":"Ali Fahimniya, Hossein Dehghani, Kishor Bharti, Sheryl Mathew, Alicia J. Kollár, Alexey V. Gorshkov, Michael J. Gullans","doi":"10.22331/q-2025-09-05-1849","DOIUrl":"https://doi.org/10.22331/q-2025-09-05-1849","url":null,"abstract":"A central goal in quantum error correction is to reduce the overhead of fault-tolerant quantum computing by increasing noise thresholds and reducing the number of physical qubits required to sustain a logical qubit. We introduce a potential path towards this goal based on a family of dynamically generated quantum error correcting codes that we call \"hyperbolic Floquet codes.'' These codes are defined by a specific sequence of non-commuting two-body measurements arranged periodically in time that stabilize a topological code on a hyperbolic manifold with negative curvature. We focus on a family of lattices for $n$ qubits that, according to our prescription that defines the code, provably achieve a finite encoding rate $(1/8+2/n)$ while still requiring only two-body measurements. Similar to hyperbolic surface codes, the distance of the code at each time-step scales at most logarithmically in $n$. The family of lattices we choose indicates that this scaling is achievable in practice. We develop and benchmark an efficient matching-based decoder that provides evidence of a threshold near 0.1% in a phenomenological noise model and 0.25% in an entangling measurements noise model. Utilizing weight-two check operators and a qubit connectivity of 3, one of our hyperbolic Floquet codes uses 400 physical qubits to encode 52 logical qubits with a code distance of 8, i.e., it is a $[[400,52,8]]$ code. At small error rates, comparable logical error suppression to this code requires 5x as many physical qubits (1924) when using the honeycomb Floquet code with the same noise model and decoder.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"8 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144995525","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

Towards violations of Local Friendliness with quantum computers 违反量子计算机的局部友好性

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-05 DOI: 10.22331/q-2025-09-05-1851

William J. Zeng, Farrokh Labib, Vincent Russo

{"title":"Towards violations of Local Friendliness with quantum computers","authors":"William J. Zeng, Farrokh Labib, Vincent Russo","doi":"10.22331/q-2025-09-05-1851","DOIUrl":"https://doi.org/10.22331/q-2025-09-05-1851","url":null,"abstract":"Local Friendliness (LF) inequalities follow from seemingly reasonable assumptions about reality: (i) “absoluteness of observed events'' (e.g., every observed event happens for all observers) and (ii) “local agency'' (e.g., free choices can be made uncorrelated with other events outside their future light cone). Extended Wigner's Friend Scenario (EWFS) thought experiments show that textbook quantum mechanics violates these inequalities. Thus, experimental evidence of these violations would make these two assumptions incompatible. In [Nature Physics 16, 1199 (2020)], the authors experimentally implemented an EWFS, using a photonic qubit to play the role of each of the “friends'' and measured violations of LF. One may question whether a photonic qubit is a physical system that counts as an “observer'' and thereby question whether the experiment's outcome is significant. Intending to measure increasingly meaningful violations, we propose using a statistical measure called the “branch factor'' to quantify the “observerness'' of the system. We then encode the EWFS as a quantum circuit such that the components of the circuit that define the friend are quantum systems of increasing branch factor. We run this circuit on quantum simulators and hardware devices, observing LF violations as the system sizes scale. As errors in quantum computers reduce the significance of the violations, better quantum computers can produce better violations. Our results extend the state of the art in proof-of-concept experimental violations from branch factor 0.0 to branch factor 16.0. This is an initial result in an experimental program for measuring LF violations at increasingly meaningful branch factors using increasingly more powerful quantum processors and networks. We introduce this program as a fundamental science application for near-term and developing quantum technology.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"163 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144995526","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

A Theory of Direct Randomized Benchmarking 直接随机基准理论

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-05 DOI: 10.22331/q-2025-09-05-1848

Anthony M. Polloreno, Arnaud Carignan-Dugas, Jordan Hines, Robin Blume-Kohout, Kevin Young, Timothy Proctor

{"title":"A Theory of Direct Randomized Benchmarking","authors":"Anthony M. Polloreno, Arnaud Carignan-Dugas, Jordan Hines, Robin Blume-Kohout, Kevin Young, Timothy Proctor","doi":"10.22331/q-2025-09-05-1848","DOIUrl":"https://doi.org/10.22331/q-2025-09-05-1848","url":null,"abstract":"Randomized benchmarking (RB) protocols are widely used to measure an average error rate for a set of quantum logic gates. However, the standard version of RB is limited because it only benchmarks a processor's native gates indirectly, by using them in composite $n$-qubit Clifford gates. Standard RB's reliance on $n$-qubit Clifford gates restricts it to the few-qubit regime, because the fidelity of a typical composite $n$-qubit Clifford gate decreases rapidly with increasing $n$. Furthermore, although standard RB is often used to infer the error rate of native gates, by rescaling standard RB's error per Clifford to an error per native gate, this is an unreliable extrapolation. Direct RB is a method that addresses these limitations of standard RB, by directly benchmarking a customizable gate set, such as a processor's native gates. Here we provide a detailed introduction to direct RB, we discuss how to design direct RB experiments, and we present two complementary theories for direct RB. The first of these theories uses the concept of error propagation or scrambling in random circuits to show that direct RB is reliable for gates that experience stochastic Pauli errors. We prove that the direct RB decay is a single exponential, and that the decay rate is equal to the average infidelity of the benchmarked gates, under broad circumstances. This theory shows that group twirling is not required for reliable RB. Our second theory proves that direct RB is reliable for gates that experience general gate-dependent Markovian errors, using similar techniques to contemporary theories for standard RB. Our two theories for direct RB have complementary regimes of applicability, and they provide complementary perspectives on why direct RB works. Together these theories provide comprehensive guarantees on the reliability of direct RB.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"34 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144995524","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

Simultaneous symmetry breaking in spontaneous Floquet states: temporal Floquet-Nambu-Goldstone modes, Floquet thermodynamics, and the time operator 自发Floquet态的同时对称破缺：时间Floquet- nambu - goldstone模式，Floquet热力学和时间算符

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-05 DOI: 10.22331/q-2025-09-05-1850

Juan Ramón Muñoz de Nova, Fernando Sols

{"title":"Simultaneous symmetry breaking in spontaneous Floquet states: temporal Floquet-Nambu-Goldstone modes, Floquet thermodynamics, and the time operator","authors":"Juan Ramón Muñoz de Nova, Fernando Sols","doi":"10.22331/q-2025-09-05-1850","DOIUrl":"https://doi.org/10.22331/q-2025-09-05-1850","url":null,"abstract":"We study simultaneous symmetry breaking in spontaneous Floquet states, focusing on the specific case of an atomic condensate. We first describe the quantization of the Nambu-Goldstone (NG) modes for a stationary state simultaneously breaking several symmetries of the Hamiltonian by invoking the generalized Gibbs ensemble, which enables a thermodynamical description of the problem. The quantization procedure involves a Berry-Gibbs connection, which depends on the macroscopic conserved charges associated to each broken symmetry and whose curvature is not invariant under generalized gauge transformations. We extend the formalism to Floquet states, where Goldstone theorem translates into the emergence of Floquet-Nambu-Goldstone (FNG) modes with zero quasi-energy. In the case of a spontaneous Floquet state, there is a genuine temporal FNG mode arising from the continuous time-translation symmetry breaking, whose quantum amplitude provides a rare realization of a time operator in Quantum Mechanics. Furthermore, since they conserve energy, spontaneous Floquet states can be shown to possess a conserved Floquet charge. Conventional Floquet systems also admit a thermodynamic description in terms of the Floquet enthalpy, the Legendre transform of the energy with respect to the Floquet charge, as these operate at fixed frequency. We apply our formalism to a particular realization of spontaneous Floquet state, the CES state, which breaks $U(1)$ and time-translation symmetries, representing a time supersolid. We numerically compute its density-density correlations, predicted to be dominated by the temporal FNG mode at long times, observing a remarkable agreement between simulation and theory. Based on these results, we propose a feasible experimental scheme to observe the temporal FNG mode of the CES state.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"48 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144995227","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

$su(d)$-squeezing and many-body entanglement geometry in finite-dimensional systems 有限维系统中的$su(d)$-挤压和多体纠缠几何

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-03 DOI: 10.22331/q-2025-09-03-1844

Giuseppe Vitagliano, Otfried Gühne, Géza Tóth

{"title":"$su(d)$-squeezing and many-body entanglement geometry in finite-dimensional systems","authors":"Giuseppe Vitagliano, Otfried Gühne, Géza Tóth","doi":"10.22331/q-2025-09-03-1844","DOIUrl":"https://doi.org/10.22331/q-2025-09-03-1844","url":null,"abstract":"Generalizing the well-known spin-squeezing inequalities, we study the relation between squeezing of collective $N$-particle $su(d)$ operators and many-body entanglement geometry in multi-particle systems. For that aim, we define the set of pseudo-separable states, which are mixtures of products of single-particle states that lie in the $(d^2-1)$-dimensional Bloch sphere but are not necessarily positive semidefinite. We obtain a set of necessary conditions for states of $N$ qudits to be of the above form. Any state that violates these conditions is entangled. We also define a corresponding $su(d)$-squeezing parameter that can be used to detect entanglement in large particle ensembles. Geometrically, this set of conditions defines a convex set of points in the space of first and second moments of the collective $N$-particle $su(d)$ operators. We prove that, in the limit $Ngg 1$, such set is filled by pseudo-separable states, while any state corresponding to a point outside of this set is necessarily entangled. We also study states that are detected by these inequalities: We show that states with a bosonic symmetry are detected if and only if the two-body reduced state violates the positive partial transpose (PPT) criterion. On the other hand, highly mixed states states close to the $su(d)$ singlet are detected which have a separable two-body reduced state and are also PPT with respect to all possible bipartitions. We also provide numerical examples of thermal equilibrium states that are detected by our set of inequalities, comparing the spin-squeezing inequalities with the $su(3)$-squeezing inequalities.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"104 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144930790","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

Efficient fault-tolerant code switching via one-way transversal CNOT gates 通过单向横向CNOT门实现高效的容错码切换

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-03 DOI: 10.22331/q-2025-09-03-1846

Sascha Heußen, Janine Hilder

{"title":"Efficient fault-tolerant code switching via one-way transversal CNOT gates","authors":"Sascha Heußen, Janine Hilder","doi":"10.22331/q-2025-09-03-1846","DOIUrl":"https://doi.org/10.22331/q-2025-09-03-1846","url":null,"abstract":"Code switching is an established technique that facilitates a universal set of FT quantum gate operations by combining two QEC codes with complementary sets of gates, which each by themselves are easy to implement fault-tolerantly. In this work, we present a code switching scheme that respects the constraints of FT circuit design by only making use of transversal gates. These gates are intrinsically FT without additional qubit overhead. We analyze application of the scheme to low-distance color codes, which are suitable for operation in existing quantum processors, for instance based on trapped ions or neutral atoms. We briefly discuss connectivity constraints that arise for architectures based on superconducting qubits. Numerical simulations of circuit-level noise indicate that a logical $T$-gate, facilitated by our scheme, could outperform both flag-FT magic state injection protocols and a physical $T$-gate at low physical error rates. Transversal code switching naturally scales to code pairs of arbitrary code distance. We observe improved performance of a distance-5 protocol compared to both the distance-3 implementation and the physical gate for realistically attainable physical entangling gate error rates. We discuss how the scheme can be implemented with a large degree of parallelization, provided that logical auxiliary qubits can be prepared reliably enough. Our logical $T$-gate circumvents potentially costly magic state factories. The requirements to perform QEC and to achieve an FT universal gate set are then essentially the same: Prepare logical auxiliary qubits offline, execute transversal gates and perform fast-enough measurements. Transversal code switching thus serves to enable more practical hardware realizations of FT universal quantum computation. The scheme alleviates resource requirements for experimental demonstrations of quantum algorithms run on logical qubits.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"99 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144930794","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