IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-15 DOI: 10.22331/q-2025-05-15-1744

Kenneth Goodenough, Tim Coopmans, Don Towsley

{"title":"On noise in swap ASAP repeater chains: exact analytics, distributions and tight approximations","authors":"Kenneth Goodenough, Tim Coopmans, Don Towsley","doi":"10.22331/q-2025-05-15-1744","DOIUrl":"https://doi.org/10.22331/q-2025-05-15-1744","url":null,"abstract":"Losses are one of the main bottlenecks for the distribution of entanglement in quantum networks, which can be overcome by the implementation of quantum repeaters. The most basic form of a quantum repeater chain is the swap ASAP repeater chain. In such a repeater chain, elementary links are probabilistically generated and deterministically swapped as soon as two adjacent links have been generated. As each entangled state is waiting to be swapped, decoherence is experienced, turning the fidelity of the entangled state between the end nodes of the chain into a random variable. Fully characterizing the (average) fidelity as the repeater chain grows is still an open problem. Here, we analytically investigate the case of equally-spaced repeaters, where we find exact analytic formulae for all moments of the fidelity up to 25 segments. We obtain these formulae by providing a general solution in terms of a $textit{generating function}$; a function whose n'th term in its Maclaurin series yields the moments of the fidelity for n segments. We generalize this approach as well to a $textit{global cut-off}$ policy – a method for increasing fidelity at the cost of longer entanglement delivery times – allowing for fast optimization of the cut-off parameter by eliminating the need for Monte Carlo simulation. We furthermore find simple approximations of the average fidelity that are exponentially tight, and, for up to 10 segments, the full distribution of the delivered fidelity. We use this to analytically calculate the secret-key rate, both with and without binning methods.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"13 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143979906","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

Block encoding bosons by signal processing 用信号处理对玻色子进行分组编码

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-15 DOI: 10.22331/q-2025-05-15-1747

Christopher F. Kane, Siddharth Hariprakash, Neel S. Modi, Michael Kreshchuk, Christian W Bauer

{"title":"Block encoding bosons by signal processing","authors":"Christopher F. Kane, Siddharth Hariprakash, Neel S. Modi, Michael Kreshchuk, Christian W Bauer","doi":"10.22331/q-2025-05-15-1747","DOIUrl":"https://doi.org/10.22331/q-2025-05-15-1747","url":null,"abstract":"Block Encoding (BE) is a crucial subroutine in many modern quantum algorithms, including those with near-optimal scaling for simulating quantum many-body systems, which often rely on Quantum Signal Processing (QSP). Currently, the primary methods for constructing BEs are the Linear Combination of Unitaries (LCU) and the sparse oracle approach. In this work, we demonstrate that QSP-based techniques, such as Quantum Singular Value Transformation (QSVT) and Quantum Eigenvalue Transformation for Unitary Matrices (QETU), can themselves be efficiently utilized for BE implementation. Specifically, we present several examples of using QSVT and QETU algorithms, along with their combinations, to block encode Hamiltonians for lattice bosons, an essential ingredient in simulations of high-energy physics. We also introduce a straightforward approach to BE based on the exact implementation of Linear Operators Via Exponentiation and LCU (LOVE-LCU). We find that, while using QSVT for BE results in the best asymptotic gate count scaling with the number of qubits per site, LOVE-LCU outperforms all other methods for operators acting on up to $lesssim11$ qubits, highlighting the importance of concrete circuit constructions over mere comparisons of asymptotic scalings. Using LOVE-LCU to implement the BE, we simulate the time evolution of single-site and two-site systems in the lattice $varphi^4$ theory using the Generalized QSP algorithm and compare the gate counts to those required for Trotter simulation.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"29 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144066457","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 detailed balance via elementary transitions 通过基本跃迁的量子详细平衡

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-15 DOI: 10.22331/q-2025-05-15-1743

Rocco Duvenhage, Kyle Oerder, Keagan van den Heuvel

引用次数: 0

Spontaneous symmetry emergence in a Hermitian system of coupled oscillators without symmetry 无对称耦合振子厄米系统中的自发对称性出现

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-15 DOI: 10.22331/q-2025-05-15-1746

T. T. Sergeev, E. S. Andrianov, A. A. Zyablovsky

引用次数: 0

Stochastic resetting in discrete-time quantum dynamics: steady states and correlations in few-qubit systems 离散时间量子动力学中的随机重置：少量子位系统中的稳态和相关性

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-13 DOI: 10.22331/q-2025-05-13-1742

Sascha Wald, Louie Hong Yao, Thierry Platini, Chris Hooley, Federico Carollo

{"title":"Stochastic resetting in discrete-time quantum dynamics: steady states and correlations in few-qubit systems","authors":"Sascha Wald, Louie Hong Yao, Thierry Platini, Chris Hooley, Federico Carollo","doi":"10.22331/q-2025-05-13-1742","DOIUrl":"https://doi.org/10.22331/q-2025-05-13-1742","url":null,"abstract":"Time evolution in several classes of quantum devices is generated through the application of quantum gates. Resetting is a critical technological feature in these systems allowing for mid-circuit measurement and complete or partial qubit reset. The possibility of realizing discrete-time reset dynamics on quantum computers makes it important to investigate the steady-state properties of such dynamics. Here, we explore the behavior of generic discrete-time unitary dynamics interspersed by random reset events. For Poissonian resets, we compute the stationary state of the process and demonstrate, by taking a weak-reset limit, the existence of \"resonances\" in the quantum gates, allowing for the emergence of steady state density matrices which are not diagonal in the eigenbasis of the generator of the unitary gate. Such resonances are a genuine discrete-time feature and impact on quantum and classical correlations even beyond the weak-reset limit. Furthermore, we consider non-Poissonian reset processes and explore conditions for the existence of a steady state. We show that, when the reset probability vanishes sufficiently rapidly with time, the system does not approach a steady state. Our results highlight key differences between continuous-time and discrete-time stochastic resetting and may be useful to engineer states with controllable correlations on existing devices.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"3 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143940279","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 and classical algorithms for nonlinear unitary dynamics 非线性酉动力学的量子和经典算法

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-13 DOI: 10.22331/q-2025-05-13-1741

Noah Brustle, Nathan Wiebe

{"title":"Quantum and classical algorithms for nonlinear unitary dynamics","authors":"Noah Brustle, Nathan Wiebe","doi":"10.22331/q-2025-05-13-1741","DOIUrl":"https://doi.org/10.22331/q-2025-05-13-1741","url":null,"abstract":"Quantum algorithms for Hamiltonian simulation and linear differential equations more generally have provided promising exponential speed-ups over classical computers on a set of problems with high real-world interest. However, extending this to a nonlinear problem has proven challenging, with exponential lower bounds having been demonstrated for the time scaling. We provide a quantum algorithm matching these bounds. Specifically, we find that for a non-linear differential equation of the form $frac{d|urangle}{dt} = A|urangle + B|urangle^{otimes2}$ for evolution of time $T$, error tolerance $epsilon$ and $c$ dependent on the strength of the nonlinearity, the number of queries to the differential operators that approaches the scaling of the quantum lower bound of $e^{o(T|B|)}$ queries in the limit of strong non-linearity. Finally, we introduce a classical algorithm based on the Euler method allowing comparably scaling to the quantum algorithm in a restricted case, as well as a randomized classical algorithm based on path integration that acts as a true analogue to the quantum algorithm in that it scales comparably to the quantum algorithm in cases where sign problems are absent.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"51 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143940278","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

Non-onsite symmetries and quantum teleportation in split-index matrix product states 分度矩阵积态中的非现场对称性和量子隐形传态

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-12 DOI: 10.22331/q-2025-05-12-1738

David T. Stephen

{"title":"Non-onsite symmetries and quantum teleportation in split-index matrix product states","authors":"David T. Stephen","doi":"10.22331/q-2025-05-12-1738","DOIUrl":"https://doi.org/10.22331/q-2025-05-12-1738","url":null,"abstract":"We describe a class of spin chains with new physical and computational properties. On the physical side, the spin chains give examples of symmetry-protected topological phases that are defined by non-onsite symmetries, i.e., symmetries that are not a tensor product of single-site operators. These phases can be detected by string-order parameters, but notably do not exhibit entanglement spectrum degeneracy. On the computational side, the spin chains represent a new class of states that can be used to deterministically teleport information across long distances, with the novel property that the necessary classical side processing is a non-linear function of the measurement outcomes. We also give examples of states that can serve as universal resources for measurement-based quantum computation, providing the first examples of such resources without entanglement spectrum degeneracy. The key tool in our analysis is a new kind of tensor network representation which we call split-index matrix product states (SIMPS). We develop the basic formalism of SIMPS, compare them to matrix product states, show how they are better equipped to describe certain kinds of non-onsite symmetries including anomalous symmetries, and discuss how they are also well-suited to describing quantum teleportation and constrained spin chains.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"2 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143933466","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

Learning Quantum Processes with Quantum Statistical Queries 用量子统计查询学习量子过程

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-12 DOI: 10.22331/q-2025-05-12-1739

Chirag Wadhwa, Mina Doosti

引用次数: 0

Interplay between external driving, dissipation and collective effects in the Markovian and non-Markovian regimes 马尔可夫和非马尔可夫制度中外部驱动、耗散和集体效应的相互作用

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-12 DOI: 10.22331/q-2025-05-12-1740

Roie Dann

{"title":"Interplay between external driving, dissipation and collective effects in the Markovian and non-Markovian regimes","authors":"Roie Dann","doi":"10.22331/q-2025-05-12-1740","DOIUrl":"https://doi.org/10.22331/q-2025-05-12-1740","url":null,"abstract":"Understanding how external driving and dissipation jointly influence the dynamics of open quantum systems is essential for advancing the study of non-equilibrium quantum phenomena and developing quantum technologies. The present study addresses the issue by exploring the behavior of open systems in driven optical setups coupled to a bosonic field. Starting from an exact non-Markovian master equation for linear systems, we extend the analysis to an ensemble of quantum emitters and validate the proposed solution. The analytical results unveil a range of intriguing phenomena, including pronounced non-Markovian corrections to the coherent driving and a collective cross-driving effect. These effects are experimentally accessible in platforms such as cavity QED, photonic crystals, and state-dependent optical lattices. In the Markovian limit, comparison with exact solutions reveal short-time non-Markovian effects that endure well beyond the environmental correlation decay time, alongside memory effects triggered by short laser pulses. These findings offer valuable insights into the dynamics of driven open systems, laying the groundwork for precise quantum state control.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"79 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143933470","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

Memory attacks in network nonlocality and self-testing 网络非局部性和自测试中的内存攻击

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-06 DOI: 10.22331/q-2025-05-06-1735

Mirjam Weilenmann, Costantino Budroni, Miguel Navascues

引用次数: 0

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