Quantum最新文献 - Book学术

Flying Spin Qubits in Quantum Dot Arrays Driven by Spin-Orbit Interaction 量子点阵列中由自旋轨道相互作用驱动的飞行自旋微ubits

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-21 DOI: 10.22331/q-2024-11-21-1533

D. Fernández-Fernández, Yue Ban, G. Platero

引用次数: 0

Time dependent Markovian master equation beyond the adiabatic limit 超越绝热极限的时变马尔可夫主方程

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-21 DOI: 10.22331/q-2024-11-21-1534

Giovanni Di Meglio, Martin B. Plenio, Susana F. Huelga

{"title":"Time dependent Markovian master equation beyond the adiabatic limit","authors":"Giovanni Di Meglio, Martin B. Plenio, Susana F. Huelga","doi":"10.22331/q-2024-11-21-1534","DOIUrl":"https://doi.org/10.22331/q-2024-11-21-1534","url":null,"abstract":"We derive a Markovian master equation that models the evolution of systems subject to driving and control fields. Our approach combines time rescaling and weak-coupling limits for the system-environment interaction with a secular approximation. The derivation makes use of the adiabatic time-evolution operator in a manner that allows for the efficient description of strong driving, while recovering the well-known adiabatic master equation in the appropriate limit. To illustrate the effectiveness of our approach, firstly we apply it to the paradigmatic case of a two-level (qubit) system subject to a form of periodic driving that remains unsolvable using a Floquet representation and lastly we extend this scenario to the situation of two interacting qubits, the first driven while the second one directly in contact with the environment. We demonstrate the reliability and broad scope of our approach by benchmarking the solutions of the derived reduced time evolution against numerically exact simulations using tensor networks. Our results provide rigorous conditions that must be satisfied by phenomenological master equations for driven systems that do not rely on first-principles derivations.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"11 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142678476","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

Grover Speedup from Many Forms of the Zeno Effect 多种形式的芝诺效应带来的格罗弗提速

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-20 DOI: 10.22331/q-2024-11-20-1532

Jesse Berwald, Nicholas Chancellor, Raouf Dridi

{"title":"Grover Speedup from Many Forms of the Zeno Effect","authors":"Jesse Berwald, Nicholas Chancellor, Raouf Dridi","doi":"10.22331/q-2024-11-20-1532","DOIUrl":"https://doi.org/10.22331/q-2024-11-20-1532","url":null,"abstract":"It has previously been established that adiabatic quantum computation, operating based on a continuous Zeno effect due to dynamical phases between eigenstates, is able to realise an optimal Grover-like quantum speedup. In other words, is able to solve an unstructured search problem with the same $sqrt{N}$ scaling as Grover's original algorithm. A natural question is whether other manifestations of the Zeno effect can also support an optimal speedup in a physically realistic model (through direct analogue application rather than indirectly by supporting a universal gateset). In this paper we show that they can support such a speedup, whether due to measurement, decoherence, or even decay of the excited state into a computationally useless state. Our results also suggest a wide variety of methods to realise speedup which do not rely on Zeno behaviour. We group these algorithms into three families to facilitate a structured understanding of how speedups can be obtained: one based on phase kicks, containing adiabatic computation and continuous-time quantum walks; one based on dephasing and measurement; and finally one based on destruction of the amplitude within the excited state, for which we are not aware of any previous results. These results suggest that there may be exciting opportunities for new paradigms of analog quantum computing based on these effects.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"35 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142678472","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

Construction of perfect tensors using biunimodular vectors 利用双模向量构建完美张量

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-20 DOI: 10.22331/q-2024-11-20-1528

Suhail Ahmad Rather

引用次数: 0

Inevitability of knowing less than nothing 一无所知的必然性

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-20 DOI: 10.22331/q-2024-11-20-1529

Gilad Gour, Mark M. Wilde, S. Brandsen, Isabelle Jianing Geng

{"title":"Inevitability of knowing less than nothing","authors":"Gilad Gour, Mark M. Wilde, S. Brandsen, Isabelle Jianing Geng","doi":"10.22331/q-2024-11-20-1529","DOIUrl":"https://doi.org/10.22331/q-2024-11-20-1529","url":null,"abstract":"A colloquial interpretation of entropy is that it is the knowledge gained upon learning the outcome of a random experiment. Conditional entropy is then interpreted as the knowledge gained upon learning the outcome of one random experiment after learning the outcome of another, possibly statistically dependent, random experiment. In the classical world, entropy and conditional entropy take only non-negative values, consistent with the intuition that one has regarding the aforementioned interpretations. However, for certain entangled states, one obtains negative values when evaluating commonly accepted and information-theoretically justified formulas for the quantum conditional entropy, leading to the confounding conclusion that one can know less than nothing in the quantum world. Here, we introduce a physically motivated framework for defining quantum conditional entropy, based on two simple postulates inspired by the second law of thermodynamics (non-decrease of entropy) and extensivity of entropy, and we argue that all plausible definitions of quantum conditional entropy should respect these two postulates. We then prove that all plausible quantum conditional entropies take on negative values for certain entangled states, so that it is inevitable that one can know less than nothing in the quantum world. All of our arguments are based on constructions of physical processes that respect the first postulate, the one inspired by the second law of thermodynamics.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"99 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673919","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

Constant-depth circuits for Boolean functions and quantum memory devices using multi-qubit gates 使用多量子比特门的布尔函数恒深电路和量子存储器件

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-20 DOI: 10.22331/q-2024-11-20-1530

Jonathan Allcock, Jinge Bao, Joao F. Doriguello, Alessandro Luongo, Miklos Santha

{"title":"Constant-depth circuits for Boolean functions and quantum memory devices using multi-qubit gates","authors":"Jonathan Allcock, Jinge Bao, Joao F. Doriguello, Alessandro Luongo, Miklos Santha","doi":"10.22331/q-2024-11-20-1530","DOIUrl":"https://doi.org/10.22331/q-2024-11-20-1530","url":null,"abstract":"We explore the power of the unbounded Fan-Out gate and the Global Tunable gates generated by Ising-type Hamiltonians in constructing constant-depth quantum circuits, with particular attention to quantum memory devices. We propose two types of constant-depth constructions for implementing Uniformly Controlled Gates. These gates include the Fan-In gates defined by $|xrangle|branglemapsto |xrangle|boplus f(x)rangle$ for $xin{0,1}^n$ and $bin{0,1}$, where $f$ is a Boolean function. The first of our constructions is based on computing the one-hot encoding of the control register $|xrangle$, while the second is based on Boolean analysis and exploits different representations of $f$ such as its Fourier expansion. Via these constructions, we obtain constant-depth circuits for the quantum counterparts of read-only and read-write memory devices – Quantum Random Access Memory (QRAM) and Quantum Random Access Gate (QRAG) – of memory size $n$. The implementation based on one-hot encoding requires either $O(nlog^{(d)}{n}log^{(d+1)}{n})$ ancillae and $O(nlog^{(d)}{n})$ Fan-Out gates or $O(nlog^{(d)}{n})$ ancillae and $16d-10$ Global Tunable gates, where $d$ is any positive integer and $log^{(d)}{n} = logcdots log{n}$ is the $d$-times iterated logarithm. On the other hand, the implementation based on Boolean analysis requires $8d-6$ Global Tunable gates at the expense of $O(n^{1/(1-2^{-d})})$ ancillae.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"35 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673920","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 proving the robustness of algorithms for early fault-tolerant quantum computers 论证早期容错量子计算机算法的鲁棒性

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-20 DOI: 10.22331/q-2024-11-20-1531

Rutuja Kshirsagar, Amara Katabarwa, Peter D. Johnson

{"title":"On proving the robustness of algorithms for early fault-tolerant quantum computers","authors":"Rutuja Kshirsagar, Amara Katabarwa, Peter D. Johnson","doi":"10.22331/q-2024-11-20-1531","DOIUrl":"https://doi.org/10.22331/q-2024-11-20-1531","url":null,"abstract":"The hope of the quantum computing field is that quantum architectures are able to scale up and realize fault-tolerant quantum computing. Due to engineering challenges, such ''cheap'' error correction may be decades away. In the meantime, we anticipate an era of ''costly'' error correction, or $textit{early fault-tolerant quantum computing}$. Costly error correction might warrant settling for error-prone quantum computations. This motivates the development of quantum algorithms which are robust to some degree of error as well as methods to analyze their performance in the presence of error. Several such algorithms have recently been developed; what is missing is a methodology to analyze their robustness. To this end, we introduce a randomized algorithm for the task of phase estimation and give an analysis of its performance under two simple noise models. In both cases the analysis leads to a noise threshold, below which arbitrarily high accuracy can be achieved by increasing the number of samples used in the algorithm. As an application of this general analysis, we compute the maximum ratio of the largest circuit depth and the dephasing scale such that performance guarantees hold. We calculate that the randomized algorithm can succeed with arbitrarily high probability as long as the required circuit depth is less than 0.916 times the dephasing scale.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"6 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142678473","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

Combinatorial NLTS From the Overlap Gap Property 从重叠间隙特性看组合无穷大系统

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-19 DOI: 10.22331/q-2024-11-19-1527

Eric R. Anschuetz, David Gamarnik, Bobak Kiani

{"title":"Combinatorial NLTS From the Overlap Gap Property","authors":"Eric R. Anschuetz, David Gamarnik, Bobak Kiani","doi":"10.22331/q-2024-11-19-1527","DOIUrl":"https://doi.org/10.22331/q-2024-11-19-1527","url":null,"abstract":"In an important recent development, Anshu, Breuckmann, and Nirkhe [3] resolved positively the so-called No Low-Energy Trivial State (NLTS) conjecture by Freedman and Hastings. The conjecture postulated the existence of linear-size local Hamiltonians on n qubit systems for which no near-ground state can be prepared by a shallow (sublogarithmic depth) circuit. The construction in [3] is based on recently developed good quantum codes. Earlier results in this direction included the constructions of the so-called Combinatorial NLTS – a weaker version of NLTS – where a state is defined to have low energy if it violates at most a vanishing fraction of the Hamiltonian terms [2]. These constructions were also based on codes.<br/> In this paper we provide a \"non-code\" construction of a class of Hamiltonians satisfying the Combinatorial NLTS. The construction is inspired by one in [2], but our proof uses the complex solution space geometry of random K-SAT instead of properties of codes. Specifically, it is known that above a certain clause-to-variables density the set of satisfying assignments of random K-SAT exhibits an overlap gap property, which implies that it can be partitioned into exponentially many clusters each constituting at most an exponentially small fraction of the total set of satisfying solutions. We establish a certain robust version of this clustering property for the space of near-satisfying assignments and show that for our constructed Hamiltonians every combinatorial near-ground state induces a near-uniform distribution supported by this set. Standard arguments then are used to show that such distributions cannot be prepared by quantum circuits with depth o(log n). Since the clustering property is exhibited by many random structures, including proper coloring and maximum cut, we anticipate that our approach is extendable to these models as well.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"69 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142670912","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

Grothendieck inequalities characterize converses to the polynomial method 格罗根第克不等式是多项式方法会话的特征

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-18 DOI: 10.22331/q-2024-11-18-1526

Jop Briët, Francisco Escudero Gutiérrez, Sander Gribling

引用次数: 0

Ground and Excited States from Ensemble Variational Principles 从集合变分原理看基态和激发态

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2024-11-14 DOI: 10.22331/q-2024-11-14-1525

Lexin Ding, Cheng-Lin Hong, Christian Schilling

{"title":"Ground and Excited States from Ensemble Variational Principles","authors":"Lexin Ding, Cheng-Lin Hong, Christian Schilling","doi":"10.22331/q-2024-11-14-1525","DOIUrl":"https://doi.org/10.22331/q-2024-11-14-1525","url":null,"abstract":"The extension of the Rayleigh-Ritz variational principle to ensemble states $rho_{mathbf{w}}equivsum_k w_k |Psi_krangle langlePsi_k|$ with fixed weights $w_k$ lies ultimately at the heart of several recent methodological developments for targeting excitation energies by variational means. Prominent examples are density and density matrix functional theory, Monte Carlo sampling, state-average complete active space self-consistent field methods and variational quantum eigensolvers. In order to provide a sound basis for all these methods and to improve their current implementations, we prove the validity of the underlying critical hypothesis: Whenever the ensemble energy is well-converged, the same holds true for the ensemble state $rho_{mathbf{w}}$ as well as the individual eigenstates $|Psi_krangle$ and eigenenergies $E_k$. To be more specific, we derive linear bounds $d_-Delta{E}_{mathbf{w}} leq Delta Q leq d_+ Delta{E}_{mathbf{w}}$ on the errors $Delta Q $ of these sought-after quantities. A subsequent analytical analysis and numerical illustration proves the tightness of our universal inequalities. Our results and particularly the explicit form of $d_{pm}equiv d_{pm}^{(Q)}(mathbf{w},mathbf{E})$ provide valuable insights into the optimal choice of the auxiliary weights $w_k$ in practical applications.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"30 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2024-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142637459","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