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Quantum memory assisted observable estimation
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-03-06 DOI: 10.22331/q-2025-03-06-1655
Liubov A. Markovich, Attaallah Almasi, Sina Zeytinoğlu, Johannes Borregaard
{"title":"Quantum memory assisted observable estimation","authors":"Liubov A. Markovich, Attaallah Almasi, Sina Zeytinoğlu, Johannes Borregaard","doi":"10.22331/q-2025-03-06-1655","DOIUrl":"https://doi.org/10.22331/q-2025-03-06-1655","url":null,"abstract":"The estimation of many-qubit observables is an essential task of quantum information processing. The generally applicable approach is to decompose the observables into weighted sums of multi-qubit Pauli strings, i.e., tensor products of single-qubit Pauli matrices, which can readily be measured with low-depth Clifford circuits. The accumulation of shot noise in this approach, however, severely limits the achievable variance for a finite number of measurements. We introduce a novel method, dubbed $textit{coherent Pauli summation}$ (CPS), that circumvents this limitation by exploiting access to a single-qubit quantum memory in which measurement information can be stored and accumulated. CPS offers a reduction in the required number of measurements for a given variance that scales linearly with the number of Pauli strings in the decomposed observable. Our work demonstrates how a single long-coherence qubit memory can assist the operation of many-qubit quantum devices in a cardinal task.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"8 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143560623","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
Seedless extractors for device-independent quantum cryptography
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-03-06 DOI: 10.22331/q-2025-03-06-1654
Cameron Foreman, Lluis Masanes
{"title":"Seedless extractors for device-independent quantum cryptography","authors":"Cameron Foreman, Lluis Masanes","doi":"10.22331/q-2025-03-06-1654","DOIUrl":"https://doi.org/10.22331/q-2025-03-06-1654","url":null,"abstract":"Device-independent (DI) quantum cryptography aims at providing secure cryptography with minimal trust in, or characterisation of, the underlying quantum devices. A key step in DI protocols is randomness extraction (or privacy amplification), which typically requires a $seed$ of additional bits with sufficient entropy and statistical independence from any bits generated during the protocol. In this work, we propose a method for extraction in DI protocols that does not require a seed and is secure against computationally unbounded quantum adversaries. The core idea is to use the Bell violation of the raw data, rather than its min-entropy, as the extractor promise. We present a complete security proof in a model where the experiment uses memoryless measurement devices acting on an arbitrary joint (across all rounds) state. Our results mark a first step in this alternative, seedless, approach to extraction in DI protocols.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"29 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561276","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
Ultrastrong coupling, nonselective measurement and quantum Zeno dynamics
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-03-06 DOI: 10.22331/q-2025-03-06-1656
Stefano Marcantoni, Marco Merkli
{"title":"Ultrastrong coupling, nonselective measurement and quantum Zeno dynamics","authors":"Stefano Marcantoni, Marco Merkli","doi":"10.22331/q-2025-03-06-1656","DOIUrl":"https://doi.org/10.22331/q-2025-03-06-1656","url":null,"abstract":"We study the dynamics of an open quantum system linearly coupled to a bosonic reservoir. We show that, in the ultrastrong coupling limit, the system undergoes a nonselective measurement and then evolves unitarily according to an effective Zeno Hamiltonian. This dynamical process is largely independent of the reservoir state. We examine the entanglement breaking effect of the ultrastrong coupling on the system. We also derive the evolution equation for systems in contact with several reservoirs when one coupling is ultrastrong. The effective system dynamics displays a rich structure and, contrarily to the single reservoir case, it is generally non-Markovian. Our approach is based on a Dyson series expansion, in which we can take the ultrastrong limit termwise, and a subsequent resummation of the series. Our derivation is mathematically rigorous and uncomplicated.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"15 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143560624","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
Chaos and magic in the dissipative quantum kicked top
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-03-05 DOI: 10.22331/q-2025-03-05-1653
Gianluca Passarelli, Procolo Lucignano, Davide Rossini, Angelo Russomanno
{"title":"Chaos and magic in the dissipative quantum kicked top","authors":"Gianluca Passarelli, Procolo Lucignano, Davide Rossini, Angelo Russomanno","doi":"10.22331/q-2025-03-05-1653","DOIUrl":"https://doi.org/10.22331/q-2025-03-05-1653","url":null,"abstract":"We consider an infinite-range interacting quantum spin-1/2 model, undergoing periodic kicking and dissipatively coupled with an environment. In the thermodynamic limit, it is described by classical mean-field equations that can show regular and chaotic regimes. At finite size, we describe the system dynamics using stochastic quantum trajectories. We find that the asymptotic nonstabilizerness (alias the $magic$, a measure of quantum complexity), averaged over trajectories, mirrors to some extent the classical chaotic behavior, while the entanglement entropy has no relation with chaos in the thermodynamic limit.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"28 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143560622","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
Device independent security of quantum key distribution from monogamy-of-entanglement games
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-03-05 DOI: 10.22331/q-2025-03-05-1652
Enrique Cervero-Martí­n, Marco Tomamichel
{"title":"Device independent security of quantum key distribution from monogamy-of-entanglement games","authors":"Enrique Cervero-Martí­n, Marco Tomamichel","doi":"10.22331/q-2025-03-05-1652","DOIUrl":"https://doi.org/10.22331/q-2025-03-05-1652","url":null,"abstract":"We analyse two party non-local games whose predicate requires Alice and Bob to generate matching bits, and their three party extensions where a third player receives all inputs and is required to output a bit that matches that of the original players. We propose a general device independent quantum key distribution protocol for the subset of such non-local games that satisfy a monogamy-of-entanglement property characterised by a gap in the maximum winning probability between the bipartite and tripartite versions of the game. This gap is due to the optimal strategy for two players requiring entanglement, which due to its monogamy property cannot be shared with any additional players. Based solely on the monogamy-of-entanglement property, we provide a simple proof of information theoretic security of our protocol. Lastly, we numerically optimize the finite and asymptotic secret key rates of our protocol using the magic square game as an example, for which we provide a numerical bound on the maximal tripartite quantum winning probability which closely matches the bipartite classical winning probability. Further, we show that our protocol is robust for depolarizing noise up to about $2.88%$, providing the first such bound for general attacks for magic square based quantum key distribution.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"50 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143560621","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 reversal: a general theory of coherent quantum absorbers
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-02-26 DOI: 10.22331/q-2025-02-26-1650
Mankei Tsang
{"title":"Quantum reversal: a general theory of coherent quantum absorbers","authors":"Mankei Tsang","doi":"10.22331/q-2025-02-26-1650","DOIUrl":"https://doi.org/10.22331/q-2025-02-26-1650","url":null,"abstract":"The fascinating concept of coherent quantum absorber – which can absorb any photon emitted by another system while maintaining entanglement with that system – has found diverse implications in open quantum system theory and quantum metrology. This work generalizes the concept by proposing the so-called reversal conditions for the two systems, in which a \"reverser\" coherently reverses any effect of the other system on a field. The reversal conditions are rigorously boiled down to concise formulas involving the Petz recovery map and Kraus operators, thereby generalizing as well as streamlining the existing treatments of coherent absorbers.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"28 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143507500","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
Squashed quantum non-Markovianity: a measure of genuine quantum non-Markovianity in states
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-02-26 DOI: 10.22331/q-2025-02-26-1646
Rajeev Gangwar, Tanmoy Pandit, Kaumudibikash Goswami, Siddhartha Das, Manabendra Nath Bera
{"title":"Squashed quantum non-Markovianity: a measure of genuine quantum non-Markovianity in states","authors":"Rajeev Gangwar, Tanmoy Pandit, Kaumudibikash Goswami, Siddhartha Das, Manabendra Nath Bera","doi":"10.22331/q-2025-02-26-1646","DOIUrl":"https://doi.org/10.22331/q-2025-02-26-1646","url":null,"abstract":"Quantum non-Markovianity in tripartite quantum states $rho_{ABC}$ represents a correlation between systems $A$ and $C$ when conditioned on the system $B$ and is known to have both classical and quantum contributions. However, a systematic characterization of the latter is missing. To address this, we propose a faithful measure for non-Markovianity of genuine quantum origin called squashed quantum non-Markovianity (sQNM). It is based on the quantum conditional mutual information and is defined by the left-over non-Markovianity after squashing out all non-quantum contributions. It is lower bounded by the squashed entanglement between non-conditioning systems in the reduced state and is delimited by the extendibility of either of the non-conditioning systems. We show that the sQNM is monogamous, asymptotically continuous, convex, additive on tensor-product states, and generally super-additive. We characterize genuine quantum non-Markovianity as a resource via a convex resource theory after identifying free states with vanishing sQNM and free operations that do not increase sQNM in states. We use our resource-theoretic framework to bound the rate of state transformations under free operations and to study state transformation under non-free operations; in particular, we find the quantum communication cost from Bob ($B$) to Alice ($A$) or Charlie ($C$) is lower bounded by the change in sQNM in the states. The sQNM finds operational meaning; in particular, the optimal rate of private communication in a variant of conditional one-time pad protocol is twice the sQNM. Also, the minimum deconstruction cost for a variant of quantum deconstruction protocol is given twice the sQNM of the state.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"83 1 Pt 2 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143495562","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
Border Ranks of Positive and Invariant Tensor Decompositions: Applications to Correlations
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-02-26 DOI: 10.22331/q-2025-02-26-1649
Andreas Klingler, Tim Netzer, Gemma De les Coves
{"title":"Border Ranks of Positive and Invariant Tensor Decompositions: Applications to Correlations","authors":"Andreas Klingler, Tim Netzer, Gemma De les Coves","doi":"10.22331/q-2025-02-26-1649","DOIUrl":"https://doi.org/10.22331/q-2025-02-26-1649","url":null,"abstract":"The matrix rank and its positive versions are robust for small approximations, i.e. they do not decrease under small perturbations. In contrast, the multipartite tensor rank can collapse for arbitrarily small errors, i.e. there may be a gap between rank and border rank, leading to instabilities in the optimization over sets with fixed tensor rank. Can multipartite positive ranks also collapse for small perturbations? In this work, we prove that multipartite positive and invariant tensor decompositions exhibit gaps between rank and border rank, including tensor rank purifications and cyclic separable decompositions. We also prove a correspondence between positive decompositions and membership in certain sets of multipartite probability distributions, and leverage the gaps between rank and border rank to prove that these correlation sets are not closed. It follows that testing membership of probability distributions arising from resources like translational invariant Matrix Product States is impossible in finite time. Overall, this work sheds light on the instability of ranks and the unique behavior of bipartite systems.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"1 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143506801","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
Synthesis and Arithmetic of Single Qutrit Circuits
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-02-26 DOI: 10.22331/q-2025-02-26-1647
Amolak Ratan Kalra, Michele Mosca, Dinesh Valluri
{"title":"Synthesis and Arithmetic of Single Qutrit Circuits","authors":"Amolak Ratan Kalra, Michele Mosca, Dinesh Valluri","doi":"10.22331/q-2025-02-26-1647","DOIUrl":"https://doi.org/10.22331/q-2025-02-26-1647","url":null,"abstract":"In this paper we study single qutrit circuits consisting of words over the Clifford$+mathcal{D}$ cyclotomic gate set, where $mathcal{D}=text{diag}(pmxi^{a},pmxi^{b},pmxi^{c})$, $xi$ is a primitive $9$-th root of unity and $a,b,c$ are integers. We characterize classes of qutrit unit vectors $z$ with entries in $mathbb{Z}[xi, frac{1}{chi}]$ based on the possibility of reducing their smallest denominator exponent (sde) with respect to $chi := 1 – xi,$ by acting an appropriate gate in Clifford$+mathcal{D}$. We do this by studying the notion of `derivatives mod $3$' of an arbitrary element of $mathbb{Z}[xi]$ and using it to study the smallest denominator exponent of $Hmathcal{D}z$ where $H$ is the qutrit Hadamard gate and $mathcal{D}$. In addition, we reduce the problem of finding all unit vectors of a given sde to that of finding integral solutions of a positive definite quadratic form along with some additional constraints. As a consequence we prove that the Clifford$+mathcal{D}$ gates naturally arise as gates with sde $0$ and $3$ in the group $U(3,mathbb{Z}[xi, frac{1}{chi}])$ of $3 times 3$ unitaries with entries in $mathbb{Z}[xi, frac{1}{chi}]$. We illustrate the general applicability of these methods to obtain an exact synthesis algorithm for Clifford$+R$ and recover the previously known exact synthesis algorithm of Kliuchnikov, Maslov, Mosca (2012). The framework developed to formulate qutrit gate synthesis for Clifford$+mathcal{D}$ extends to qudits of arbitrary prime power.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"3 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143495566","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
Spectral chaos bounds from scaling theory of maximally efficient quantum-dynamical scrambling
IF 6.4 2区 物理与天体物理
Quantum Pub Date : 2025-02-26 DOI: 10.22331/q-2025-02-26-1651
Tara Kalsi, Alessandro Romito, Henning Schomerus
{"title":"Spectral chaos bounds from scaling theory of maximally efficient quantum-dynamical scrambling","authors":"Tara Kalsi, Alessandro Romito, Henning Schomerus","doi":"10.22331/q-2025-02-26-1651","DOIUrl":"https://doi.org/10.22331/q-2025-02-26-1651","url":null,"abstract":"A key conjecture about the evolution of complex quantum systems towards an ergodic steady state, known as scrambling, is that this process acquires universal features when it is most efficient. We develop a single-parameter scaling theory for the spectral statistics in this scenario, which embodies exact self-similarity of the spectral correlations along the complete scrambling dynamics. We establish that the scaling predictions are matched by a privileged stochastic process and serve as bounds for other dynamical scrambling scenarios, allowing one to quantify inefficient or incomplete scrambling on all time scales.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"28 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143506802","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
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