Quantum最新文献_第2页

Knot invariants and indefinite causal order 结不变量和不定因果顺序

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-10-06 DOI: 10.22331/q-2025-10-06-1875

Samuel Fedida, Anne-Catherine de la Hamette, Viktoria Kabel, Časlav Brukner

引用次数: 0

Monitored quantum transport: full counting statistics of a quantum Hall interferometer 监测量子输运：量子霍尔干涉仪的全计数统计

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-10-02 DOI: 10.22331/q-2025-10-02-1874

C.W.J. Beenakker, Jin-Fu Chen

引用次数: 0

Backpropagation scaling in parameterised quantum circuits 参数化量子电路中的反向传播缩放

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-10-02 DOI: 10.22331/q-2025-10-02-1873

Joseph Bowles, David Wierichs, Chae-Yeun Park

{"title":"Backpropagation scaling in parameterised quantum circuits","authors":"Joseph Bowles, David Wierichs, Chae-Yeun Park","doi":"10.22331/q-2025-10-02-1873","DOIUrl":"https://doi.org/10.22331/q-2025-10-02-1873","url":null,"abstract":"The discovery of the backpropagation algorithm ranks among one of the most important moments in the history of machine learning, and has made possible the training of large-scale neural networks through its ability to compute gradients at roughly the same computational cost as model evaluation. Despite its importance, a similar backpropagation-like scaling for gradient evaluation of parameterised quantum circuits has remained elusive. Currently, the most popular method requires sampling from a number of circuits that scales with the number of circuit parameters, making training of large-scale quantum circuits prohibitively expensive in practice. Here we address this problem by introducing a class of structured circuits that are not known to be classically simulable and admit gradient estimation with significantly fewer circuits. In the simplest case – for which the parameters feed into commuting quantum gates – these circuits allow for fast estimation of the gradient, higher order partial derivatives and the Fisher information matrix. Moreover, specific families of parameterised circuits exist for which the scaling of gradient estimation is in line with classical backpropagation, and can thus be trained at scale. In a toy classification problem on 16 qubits, such circuits show competitive performance with other methods, while reducing the training cost by about two orders of magnitude.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"8 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145203429","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

Symmetry resolved out-of-time-order correlators of Heisenberg spin chains using projected matrix product operators 利用投影矩阵乘积算子对称解析海森堡自旋链的非时序相关器

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-10-01 DOI: 10.22331/q-2025-10-01-1871

Martina Gisti, David J. Luitz, Maxime Debertolis

{"title":"Symmetry resolved out-of-time-order correlators of Heisenberg spin chains using projected matrix product operators","authors":"Martina Gisti, David J. Luitz, Maxime Debertolis","doi":"10.22331/q-2025-10-01-1871","DOIUrl":"https://doi.org/10.22331/q-2025-10-01-1871","url":null,"abstract":"We extend the concept of operator charge in the context of an abelian $U(1)$ symmetry and apply this framework to symmetry-preserving matrix product operators (MPOs), enabling the description of operators projected onto specific sectors of the corresponding symmetry. Leveraging this representation, we study the effect of interactions on the scrambling of information in an integrable Heisenberg spin chain, by controlling the number of particles. Our focus lies on out-of-time order correlators (OTOCs) which we project on sectors with a fixed number of particles. This allows us to link the non-interacting system to the fully-interacting one by allowing more and more particle to interact with each other, keeping the interaction parameter fixed. While at short times, the OTOCs are almost not affected by interactions, the spreading of the information front becomes gradually faster and the OTOC saturate at larger values as the number of particle increases. We also study the behavior of finite-size systems by considering the OTOCs at times beyond the point where the front hits the boundary of the system. We find that in every sector with more than one particle, the OTOCs behave as if the local operator was rotated by a random unitary matrix, indicating that the presence of boundaries contributes to the maximal scrambling of local operators.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"37 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145195521","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

On High-Dimensional Twin-Field Quantum Key Distribution 高维双场量子密钥分配

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-10-01 DOI: 10.22331/q-2025-10-01-1869

Ronny Mueller, Mujtaba Zahidy, Leif Katsuo Oxenløwe, Søren Forchhammer, Davide Bacco

引用次数: 0

Meson dynamics from locally exciting a particle-conserving $Z_2$ lattice gauge theory 局部激发守恒粒子Z_2晶格规范理论的介子动力学

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-10-01 DOI: 10.22331/q-2025-10-01-1872

Vaibhav Sharma, Kaden R. A. Hazzard

{"title":"Meson dynamics from locally exciting a particle-conserving $Z_2$ lattice gauge theory","authors":"Vaibhav Sharma, Kaden R. A. Hazzard","doi":"10.22331/q-2025-10-01-1872","DOIUrl":"https://doi.org/10.22331/q-2025-10-01-1872","url":null,"abstract":"Quantum simulation of lattice gauge theories is an important avenue to gain insights into both particle physics phenomena and constrained quantum many-body dynamics. There is a growing interest in probing analogs of high energy collision phenomena in lattice gauge theories that can be implemented on current quantum simulators. Motivated by this, we characterize the confined mesons that originate from a local high energy excitation in a particle-conserving 1D $Z_2$ lattice gauge theory. We focus on a simple, experimentally accessible setting that does not require preparation of colliding wavepackets and isolates the effects of gauge field confinement strength and initial state energy on the nature of propagating excitations. We find that the dynamics is characterized by the propagation of a superposition of differently sized mesons. The linear confinement leads to meson size oscillations in time. The average meson size and oscillation frequency are controlled by the strength of the gauge field confinement. At a constant confinement field, the average meson length is controlled by the initial excitation's energy. Higher energies produce longer mesons and their effective mass depends strongly on their size: longer mesons propagate more slowly out of the central excitation. Mesons of different sizes get spatially filtered with time due to different speeds. We show that this phenomenology is a consequence of linear confinement and remains valid in both the strong and weak confinement limit. We present simple explanations of these phenomena supported by exact numerics.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"100 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145203434","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 entanglement of random multipartite quantum states 估计随机多部量子态的纠缠

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-10-01 DOI: 10.22331/q-2025-10-01-1870

Khurshed P. Fitter, Cécilia Lancien, Ion Nechita

{"title":"Estimating the entanglement of random multipartite quantum states","authors":"Khurshed P. Fitter, Cécilia Lancien, Ion Nechita","doi":"10.22331/q-2025-10-01-1870","DOIUrl":"https://doi.org/10.22331/q-2025-10-01-1870","url":null,"abstract":"Genuine multipartite entanglement of a given multipartite pure quantum state can be quantified through its geometric measure of entanglement, which, up to logarithms, is simply the maximum overlap of the corresponding unit tensor with product unit tensors, a quantity that is also known as the injective norm of the tensor. Our general goal in this work is to estimate this injective norm of randomly sampled tensors. To this end, we study and compare various algorithms, based either on the widely used alternating least squares method or on a novel normalized gradient descent approach, and suited to either symmetrized or non-symmetrized random tensors. We first benchmark their respective performances on the case of symmetrized real Gaussian tensors, whose asymptotic average injective norm is known analytically. Having established that our proposed normalized gradient descent algorithm generally performs best, we then use it to obtain numerical estimates for the average injective norm of complex Gaussian tensors (i.e., up to normalization, uniformly distributed multipartite pure quantum states), with or without permutation-invariance. We also estimate the average injective norm of random matrix product states constructed from Gaussian local tensors, with or without translation-invariance. All these results constitute the first numerical estimates on the amount of genuinely multipartite entanglement typically present in various models of random multipartite pure states. Finally, motivated by our numerical results, we posit two conjectures on the injective norms of random Gaussian tensors (real and complex) and Gaussian MPS in the asymptotic limit of the physical dimension.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"17 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145195520","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

Potential renormalisation, Lamb shift and mean-force Gibbs state – to shift or not to shift? 潜在重整，兰姆位移和平均力吉布斯态，移动还是不移动？

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-30 DOI: 10.22331/q-2025-09-30-1868

Luis A. Correa, Jonas Glatthard

{"title":"Potential renormalisation, Lamb shift and mean-force Gibbs state – to shift or not to shift?","authors":"Luis A. Correa, Jonas Glatthard","doi":"10.22331/q-2025-09-30-1868","DOIUrl":"https://doi.org/10.22331/q-2025-09-30-1868","url":null,"abstract":"Often, the microscopic interaction mechanism of an open quantum system gives rise to a `counter term' which renormalises the system Hamiltonian. Such term compensates for the distortion of the system's potential due to the finite coupling to the environment. Even if the coupling is weak, the counter term is, in general, not negligible. Similarly, weak-coupling master equations feature a number of `Lamb-shift terms' which, contrary to popular belief, cannot be neglected. Yet, the practice of vanishing both counter term and Lamb shift when dealing with master equations is almost universal; and, surprisingly, it can yield $better$ results. By accepting the conventional wisdom, one may approximate the dynamics more accurately and, importantly, the resulting master equation is guaranteed to equilibrate to the correct steady state in the high-temperature limit. In this paper we discuss why is this the case. Specifically, we show that, if the potential distortion is small – but non-negligible – the counter term does not influence any dissipative processes to second order in the coupling. Furthermore, we show that, for large environmental cutoff, the Lamb-shift terms approximately cancel any coherent effects due to the counter term – this renders the combination of both contributions irrelevant in practice. We thus provide precise conditions under which the open-system $folklore$ regarding Lamb shift and counter terms is rigorously justified.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"19 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145188514","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

Holevo Cramér-Rao bound: How close can we get without entangling measurements? Holevo cramsamr - rao bound：在不纠缠测量的情况下，我们能有多接近？

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-30 DOI: 10.22331/q-2025-09-30-1867

Aritra Das, Lorcán O. Conlon, Jun Suzuki, Simon K. Yung, Ping K. Lam, Syed M. Assad

{"title":"Holevo Cramér-Rao bound: How close can we get without entangling measurements?","authors":"Aritra Das, Lorcán O. Conlon, Jun Suzuki, Simon K. Yung, Ping K. Lam, Syed M. Assad","doi":"10.22331/q-2025-09-30-1867","DOIUrl":"https://doi.org/10.22331/q-2025-09-30-1867","url":null,"abstract":"In multi-parameter quantum metrology, the resource of entanglement can lead to an increase in efficiency of the estimation process. Entanglement can be used in the state preparation stage, or the measurement stage, or both, to harness this advantage; here we focus on the role of entangling measurements. Specifically, entangling or collective measurements over multiple identical copies of a probe state are known to be superior to measuring each probe individually, but the extent of this improvement is an open problem. It is also known that such entangling measurements, though resource-intensive, are required to attain the ultimate limits in multi-parameter quantum metrology and quantum information processing tasks. In this work we investigate the maximum precision improvement that collective quantum measurements can offer over individual measurements for estimating parameters of qudit states, calling this the 'collective quantum enhancement'. We show that, whereas the maximum enhancement can, in principle, be a factor of $n$ for estimating $n$ parameters, this bound is not tight for large $n$. Instead, our results prove an enhancement linear in dimension of the qudit is possible using collective measurements and lead us to conjecture that this is the maximum collective quantum enhancement in any local estimation scenario.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"95 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145188650","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

QuantumToolbox.jl: An efficient Julia framework for simulating open quantum systems QuantumToolbox。模拟开放量子系统的高效Julia框架

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-09-29 DOI: 10.22331/q-2025-09-29-1866

Alberto Mercurio, Yi-Te Huang, Li-Xun Cai, Yueh-Nan Chen, Vincenzo Savona, Franco Nori

引用次数: 0