Quantum最新文献_第8页

A Theory of Inaccessible Information 不可获取信息理论

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-09-09 DOI: 10.22331/q-2024-09-09-1464

Jacopo Surace

{"title":"A Theory of Inaccessible Information","authors":"Jacopo Surace","doi":"10.22331/q-2024-09-09-1464","DOIUrl":"https://doi.org/10.22331/q-2024-09-09-1464","url":null,"abstract":"What would be the consequences if there were fundamental limits to our ability to experimentally explore the world? In this work we seriously consider this question. We assume the existence of statements whose truth value is not experimentally accessible. That is, there is no way, not even in theory, to directly test if these statements are true or false. We further develop a theory in which experimentally accessible statements are a union of a fixed minimum number of inaccessible statements. For example, the value of truth of the statements \"a\" and \"b\" is not accessible, but the value of truth of the statement \"a or b\" is accessible. We do not directly assume probability theory, we exclusively define experimentally accessible and inaccessible statements and build on these notions using the rules of classical logic. We find that an interesting structure emerges. Developing this theory, we relax the logical structure to a probabilistic one, obtaining a theory rich in structure that we call \"theory of inaccessible information\". Surprisingly, the simplest model of theory of inaccessible information is the qubit in quantum mechanics. Along the path for the construction of this theory, we characterise and study a family of multiplicative information measures that we call \"inaccessibility measures\".","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"2 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142158686","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

Geometrical description and Faddeev-Jackiw quantization of electrical networks 电气网络的几何描述和 Faddeev-Jackiw 量化

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-09-09 DOI: 10.22331/q-2024-09-09-1466

A. Parra-Rodriguez, I. L. Egusquiza

{"title":"Geometrical description and Faddeev-Jackiw quantization of electrical networks","authors":"A. Parra-Rodriguez, I. L. Egusquiza","doi":"10.22331/q-2024-09-09-1466","DOIUrl":"https://doi.org/10.22331/q-2024-09-09-1466","url":null,"abstract":"In lumped-element electrical circuit theory, the problem of solving Maxwell's equations in the presence of media is reduced to two sets of equations, the constitutive equations encapsulating local geometry and dynamics of a confined energy density, and the Kirchhoff equations enforcing conservation of charge and energy in a larger, topological, scale. We develop a new geometric and systematic description of the dynamics of general lumped-element electrical circuits as first order differential equations, derivable from a Lagrangian and a Rayleigh dissipation function. Through the Faddeev-Jackiw method we identify and classify the singularities that arise in the search for Hamiltonian descriptions of general networks. The core of our solution relies on the correct identification of the reduced manifold in which the circuit state is expressible, e.g., a mix of flux and charge degrees of freedom, including the presence of compact ones. We apply our fully programmable method to obtain (canonically quantizable) Hamiltonian descriptions of nonlinear and nonreciprocal circuits which would be cumbersome/singular if pure node-flux or loop-charge variables were used as a starting configuration space. We also propose a specific assignment of topology for the branch variables of energetic elements, that when used as input to the procedure gives results consistent with classical descriptions as well as with spectra of more involved quantum circuits. This work unifies diverse existent geometrical pictures of electrical network theory, and will prove useful, for instance, to automatize the computation of exact Hamiltonian descriptions of superconducting quantum chips.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"15 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142158688","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

Confinement and Kink Entanglement Asymmetry on a Quantum Ising Chain 量子伊辛链上的禁闭和扭结纠缠不对称

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-09-06 DOI: 10.22331/q-2024-09-06-1462

Brian J. J. Khor, D. M. Kürkçüoglu, T. J. Hobbs, G. N. Perdue, Israel Klich

引用次数: 0

Handbook for Efficiently Quantifying Robustness of Magic 高效量化魔术鲁棒性手册

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-09-05 DOI: 10.22331/q-2024-09-05-1461

Hiroki Hamaguchi, Kou Hamada, Nobuyuki Yoshioka

{"title":"Handbook for Efficiently Quantifying Robustness of Magic","authors":"Hiroki Hamaguchi, Kou Hamada, Nobuyuki Yoshioka","doi":"10.22331/q-2024-09-05-1461","DOIUrl":"https://doi.org/10.22331/q-2024-09-05-1461","url":null,"abstract":"The nonstabilizerness, or magic, is an essential quantum resource to perform universal quantum computation. Robustness of magic (RoM) in particular characterizes the degree of usefulness of a given quantum state for non-Clifford operation. While the mathematical formalism of RoM can be given in a concise manner, it is extremely challenging to determine the RoM in practice, since it involves superexponentially many pure stabilizer states. In this work, we present efficient novel algorithms to compute the RoM. The crucial technique is a subroutine that achieves the remarkable features in calculation of overlaps between pure stabilizer states: (i) the time complexity per each stabilizer is reduced exponentially, (ii) the space complexity is reduced superexponentially. Based on this subroutine, we present algorithms to compute the RoM for arbitrary states up to $n=7$ qubits on a laptop, while brute-force methods require a memory size of 86 TiB. As a byproduct, the proposed subroutine allows us to simulate the stabilizer fidelity up to $n=8$ qubits, for which naive methods require memory size of 86 PiB so that any state-of-the-art classical computer cannot execute the computation. We further propose novel algorithms that utilize the preknowledge on the structure of target quantum state such as the permutation symmetry of disentanglement, and numerically demonstrate our state-of-the-art results for copies of magic states and partially disentangled quantum states. The series of algorithms constitute a comprehensive “handbook'' to scale up the computation of the RoM, and we envision that the proposed technique applies to the computation of other quantum resource measures as well.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"20 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142138383","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

Digital quantum simulation of lattice fermion theories with local encoding 带有局部编码的格子费米子理论的数字量子模拟

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-09-04 DOI: 10.22331/q-2024-09-04-1460

Marco Ballarin, Giovanni Cataldi, Giuseppe Magnifico, Daniel Jaschke, Marco Di Liberto, Ilaria Siloi, Simone Montangero, Pietro Silvi

引用次数: 0

Perfect quantum protractors 完美量子量角器

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-09-03 DOI: 10.22331/q-2024-09-03-1459

Michał Piotrak, Marek Kopciuch, Arash Dezhang Fard, Magdalena Smolis, Szymon Pustelny, Kamil Korzekwa

{"title":"Perfect quantum protractors","authors":"Michał Piotrak, Marek Kopciuch, Arash Dezhang Fard, Magdalena Smolis, Szymon Pustelny, Kamil Korzekwa","doi":"10.22331/q-2024-09-03-1459","DOIUrl":"https://doi.org/10.22331/q-2024-09-03-1459","url":null,"abstract":"In this paper we introduce and investigate the concept of a $textit{perfect quantum protractor}$, a pure quantum state $|psirangleinmathcal{H}$ that generates three different orthogonal bases of $mathcal{H}$ under rotations around each of the three perpendicular axes. Such states can be understood as pure states of maximal uncertainty with regards to the three components of the angular momentum operator, as we prove that they maximise various entropic and variance-based measures of such uncertainty. We argue that perfect quantum protractors can only exist for systems with a well-defined total angular momentum $j$, and we prove that they do not exist for $jin{1/2,2,5/2}$, but they do exist for $jin{1,3/2,3}$ (with numerical evidence for their existence when $j=7/2$). We also explain that perfect quantum protractors form an optimal resource for a metrological task of estimating the angle of rotation around (or the strength of magnetic field along) one of the three perpendicular axes, when the axis is not $textit{a priori}$ known. Finally, we demonstrate this metrological utility by performing an experiment with warm atomic vapours of rubidium-87, where we prepare a perfect quantum protractor for a spin-1 system, let it precess around $x$, $y$ or $z$ axis, and then employ it to optimally estimate the rotation angle.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"51 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142123503","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

Entanglement buffering with two quantum memories 利用两个量子存储器实现纠缠缓冲

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-09-03 DOI: 10.22331/q-2024-09-03-1458

Bethany Davies, Álvaro G. Iñesta, Stephanie Wehner

{"title":"Entanglement buffering with two quantum memories","authors":"Bethany Davies, Álvaro G. Iñesta, Stephanie Wehner","doi":"10.22331/q-2024-09-03-1458","DOIUrl":"https://doi.org/10.22331/q-2024-09-03-1458","url":null,"abstract":"Quantum networks crucially rely on the availability of high-quality entangled pairs of qubits, known as entangled links, distributed across distant nodes. Maintaining the quality of these links is a challenging task due to the presence of time-dependent noise, also known as decoherence. Entanglement purification protocols offer a solution by converting multiple low-quality entangled states into a smaller number of higher-quality ones. In this work, we introduce a framework to analyse the performance of entanglement buffering setups that combine entanglement consumption, decoherence, and entanglement purification. We propose two key metrics: the availability, which is the steady-state probability that an entangled link is present, and the average consumed fidelity, which quantifies the steady-state quality of consumed links. We then investigate a two-node system, where each node possesses two quantum memories: one for long-term entanglement storage, and another for entanglement generation. We model this setup as a continuous-time stochastic process and derive analytical expressions for the performance metrics. Our findings unveil a trade-off between the availability and the average consumed fidelity. We also bound these performance metrics for a buffering system that employs the well-known bilocal Clifford purification protocols. Importantly, our analysis demonstrates that, in the presence of noise, consistently purifying the buffered entanglement increases the average consumed fidelity, even when some buffered entanglement is discarded due to purification failures.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"90 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142123502","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

Tutorial: projector approach to master equations for open quantum systems 教程：开放量子系统主方程的投影仪方法

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-08-29 DOI: 10.22331/q-2024-08-29-1454

C. Gonzalez-Ballestero

{"title":"Tutorial: projector approach to master equations for open quantum systems","authors":"C. Gonzalez-Ballestero","doi":"10.22331/q-2024-08-29-1454","DOIUrl":"https://doi.org/10.22331/q-2024-08-29-1454","url":null,"abstract":"Most quantum theorists are familiar with different ways of describing the effective quantum dynamics of a system coupled to external degrees of freedom, such as the Born-Markov master equation or the adiabatic elimination. Understanding the deep connection between these -- sometimes apparently unrelated -- methods can be a powerful tool, allowing us to derive effective dynamics in unconventional systems or regimes. This tutorial aims at providing quantum theorists across multiple fields (e.g., quantum and atom optics, optomechanics, or hybrid quantum systems) with a self-contained practical toolbox to derive effective quantum dynamics, applicable to systems ranging from $N$-level emitters to mechanical resonators. First, we summarize the projector approach to open quantum systems and the derivation of the fundamental Nakajima-Zwanzig equation. Then, we show how three common effective equations, namely the Brownian master equation, the Born-Markov master equation, and the adiabatic elimination used in atom and molecular optics, can be derived from different perturbative expansions of the Nakajima-Zwanzig equation. We also solve in detail four specific examples using this formalism, namely a harmonic oscillator subject to displacement noise, the effective equations of a mechanical resonator cooled by an optical cavity, the Purcell effect for a qubit coupled to an optical cavity, and the adiabatic elimination in a Lambda system.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"127 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142090070","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

Analysis of quantum Krylov algorithms with errors 有误差的量子克雷洛夫算法分析

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-08-29 DOI: 10.22331/q-2024-08-29-1457

William Kirby

引用次数: 0

Unraveling the emergence of quantum state designs in systems with symmetry 揭示具有对称性的系统中量子态设计的出现

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-08-29 DOI: 10.22331/q-2024-08-29-1456

Naga Dileep Varikuti, Soumik Bandyopadhyay

{"title":"Unraveling the emergence of quantum state designs in systems with symmetry","authors":"Naga Dileep Varikuti, Soumik Bandyopadhyay","doi":"10.22331/q-2024-08-29-1456","DOIUrl":"https://doi.org/10.22331/q-2024-08-29-1456","url":null,"abstract":"Quantum state designs, by enabling an efficient sampling of random quantum states, play a quintessential role in devising and benchmarking various quantum protocols with broad applications ranging from circuit designs to black hole physics. Symmetries, on the other hand, are expected to reduce the randomness of a state. Despite being ubiquitous, the effects of symmetry on quantum state designs remain an outstanding question. The recently introduced projected ensemble framework generates efficient approximate state $t$-designs by hinging on projective measurements and many-body quantum chaos. In this work, we examine the emergence of state designs from the random generator states exhibiting symmetries. Leveraging on translation symmetry, we analytically establish a sufficient condition for the measurement basis leading to the state $t$-designs. Then, by making use of the trace distance measure, we numerically investigate the convergence to the designs. Subsequently, we inspect the violation of the sufficient condition to identify bases that fail to converge. We further demonstrate the emergence of state designs in a physical system by studying the dynamics of a chaotic tilted field Ising chain with translation symmetry. We find faster convergence of the trace distance during the early time evolution in comparison to the cases when the symmetry is broken. To delineate the general applicability of our results, we extend our analysis to other symmetries. We expect our findings to pave the way for further exploration of deep thermalization and equilibration of closed and open quantum many-body systems.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"94 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142090072","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