Quantum最新文献_第3页

Approximate inverse measurement channel for shallow shadows 浅阴影的近似反向测量通道

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-08 DOI: 10.22331/q-2025-04-08-1698

Riccardo Cioli, Elisa Ercolessi, Matteo Ippoliti, Xhek Turkeshi, Lorenzo Piroli

{"title":"Approximate inverse measurement channel for shallow shadows","authors":"Riccardo Cioli, Elisa Ercolessi, Matteo Ippoliti, Xhek Turkeshi, Lorenzo Piroli","doi":"10.22331/q-2025-04-08-1698","DOIUrl":"https://doi.org/10.22331/q-2025-04-08-1698","url":null,"abstract":"Classical shadows are a versatile tool to probe many-body quantum systems, consisting of a combination of randomised measurements and classical post-processing computations. In a recently introduced version of the protocol, the randomization step is performed via unitary circuits of variable depth $t$, defining the so-called shallow shadows. For sufficiently large $t$, this approach allows one to get around the use of non-local unitaries to probe global properties such as the fidelity with respect to a target state or the purity. Still, shallow shadows involve the inversion of a many-body map, the measurement channel, which requires non-trivial computations in the post-processing step, thus limiting its applicability when the number of qubits $N$ is large. In this work, we put forward a simple approximate post-processing scheme where the infinite-depth inverse channel is applied to the finite-depth classical shadows and study its performance for fidelity and purity estimation. The scheme allows for different circuit connectivity, as we illustrate for geometrically local circuits in one and two spatial dimensions and geometrically non-local circuits made of two-qubit gates. For the fidelity, we find that the resulting estimator coincides with a known linear cross-entropy, achieving an arbitrary small approximation error $delta$ at depth $t=O(log (N/delta))$ (independent of the circuit connectivity). For the purity, we show that the estimator becomes accurate at a depth $O(N)$. In addition, at those depths, the variances of both the fidelity and purity estimators display the same scaling with $N$ as in the case of global random unitaries. We establish these bounds by analytic arguments and extensive numerical computations in several cases of interest. Our work extends the applicability of shallow shadows to large system sizes and general circuit connectivity.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"89 1","pages":"1698"},"PeriodicalIF":6.4,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143798106","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

Controlling measurement-induced phase transitions with tunable detector coupling

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-08 DOI: 10.22331/q-2025-04-08-1697

Ritu Nehra, Alessandro Romito, Dganit Meidan

引用次数: 0

A Note on Quantum-Secure PRPs

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-08 DOI: 10.22331/q-2025-04-08-1696

Mark Zhandry

引用次数: 0

What can unitary sequences tell us about multi-time physics?

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-08 DOI: 10.22331/q-2025-04-08-1695

Gregory A. L. White, Felix A. Pollock, Lloyd C. L. Hollenberg, Charles D. Hill, Kavan Modi

{"title":"What can unitary sequences tell us about multi-time physics?","authors":"Gregory A. L. White, Felix A. Pollock, Lloyd C. L. Hollenberg, Charles D. Hill, Kavan Modi","doi":"10.22331/q-2025-04-08-1695","DOIUrl":"https://doi.org/10.22331/q-2025-04-08-1695","url":null,"abstract":"Multi-time quantum processes are endowed with the same richness as multipartite states, including temporal entanglement and exotic causal structures. However, experimentally probing these rich phenomena leans heavily on fast and clean mid-circuit measurements, which are rarely available. We show here how surprisingly accessible these phenomena are in nascent quantum processors even when faced with substantially limited control. We work within the limitation where only unitary control is allowed, followed by a terminating measurement. Within this setting, we first develop a witness for genuine multi-time entanglement, and then methods to bound (from top and bottom) multi-time entanglement, non-Markovianity, purity, entropy, and other correlative measures. Our tools are designed to be implemented on quantum information processors, which we proceed to demonstrate. Finally, we discuss the limitations of these methods by testing them across random multi-time processes. Conceptually, this broadens our understanding of the extent to which temporal correlations may be determined with only deterministic control. Our techniques are pertinent to generic quantum stochastic dynamical processes, with a scope ranging across condensed matter physics, quantum biology, and in-depth diagnostics of NISQ-era quantum devices.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"64 1","pages":"1695"},"PeriodicalIF":6.4,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143798373","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

Spatially-Coupled QLDPC Codes

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-07 DOI: 10.22331/q-2025-04-07-1693

Siyi Yang, Robert Calderbank

{"title":"Spatially-Coupled QLDPC Codes","authors":"Siyi Yang, Robert Calderbank","doi":"10.22331/q-2025-04-07-1693","DOIUrl":"https://doi.org/10.22331/q-2025-04-07-1693","url":null,"abstract":"Spatially-coupled (SC) codes is a class of convolutional LDPC codes that has been well investigated in classical coding theory thanks to their high performance and compatibility with low-latency decoders. We describe toric codes as quantum counterparts of classical two-dimensional spatially-coupled (2D-SC) codes, and introduce spatially-coupled quantum LDPC (SC-QLDPC) codes as a generalization. We use the convolutional structure to represent the parity check matrix of a 2D-SC code as a polynomial in two indeterminates, and derive an algebraic condition that is both necessary and sufficient for a 2D-SC code to be a stabilizer code. This algebraic framework facilitates the construction of new code families. While not the focus of this paper, we note that small memory facilitates physical connectivity of qubits, and it enables local encoding and low-latency windowed decoding. In this paper, we use the algebraic framework to optimize short cycles in the Tanner graph of 2D-SC hypergraph product (HGP) codes that arise from short cycles in either component code. While prior work focuses on QLDPC codes with rate less than 1/10, we construct 2D-SC HGP codes with small memories, higher rates (about 1/3), and superior thresholds.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"34 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143789547","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

Resource-Optimized Grouping Shadow for Efficient Energy Estimation

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-07 DOI: 10.22331/q-2025-04-07-1694

Min Li, Mao Lin, Matthew J. S. Beach

引用次数: 0

Charge and Spin Sharpening Transitions on Dynamical Quantum Trees

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-07 DOI: 10.22331/q-2025-04-07-1692

Xiaozhou Feng, Nadezhda Fishchenko, Sarang Gopalakrishnan, Matteo Ippoliti

{"title":"Charge and Spin Sharpening Transitions on Dynamical Quantum Trees","authors":"Xiaozhou Feng, Nadezhda Fishchenko, Sarang Gopalakrishnan, Matteo Ippoliti","doi":"10.22331/q-2025-04-07-1692","DOIUrl":"https://doi.org/10.22331/q-2025-04-07-1692","url":null,"abstract":"The dynamics of monitored systems can exhibit a measurement-induced phase transition (MIPT) between entangling and disentangling phases, tuned by the measurement rate. When the dynamics obeys a continuous symmetry, the entangling phase further splits into a fuzzy phase and a sharp phase based on the scaling of fluctuations of the symmetry charge. While the sharpening transition for Abelian symmetries is well understood analytically, no such understanding exists for the non- Abelian case. In this work, building on a recent analytical solution of the MIPT on tree-like circuit architectures (where qubits are repatedly added or removed from the system in a recursive pattern), we study entanglement and sharpening transitions in monitored dynamical quantum trees obeying $U(1)$ and $SU(2)$ symmetries. The recursive structure of tree tensor networks enables powerful analytical and numerical methods to determine the phase diagrams in both cases. In the $U(1)$ case, we analytically derive a Fisher-KPP-like differential equation that allows us to locate the critical point and identify its properties. We find that the entanglement/purification and sharpening transitions generically occur at distinct measurement rates. In the $SU(2)$ case, we find that the fuzzy phase is generic, and a sharp phase is possible only in the limit of maximal measurement rate. In this limit, we analytically solve the boundaries separating the fuzzy and sharp phases, and find them to be in agreement with exact numerical simulations.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"217 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143789532","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

Noise-tolerant public-key quantum money from a classical oracle

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-07 DOI: 10.22331/q-2025-04-07-1691

Peter Yuen

引用次数: 0

Nonlinearity of the Fidelity in Open Qudit Systems: Gate and Noise Dependence in High-dimensional Quantum Computing

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-07 DOI: 10.22331/q-2025-04-07-1690

Jean-Gabriel Hartmann, Denis Janković, Rémi Pasquier, Mario Ruben, Paul-Antoine Hervieux

{"title":"Nonlinearity of the Fidelity in Open Qudit Systems: Gate and Noise Dependence in High-dimensional Quantum Computing","authors":"Jean-Gabriel Hartmann, Denis Janković, Rémi Pasquier, Mario Ruben, Paul-Antoine Hervieux","doi":"10.22331/q-2025-04-07-1690","DOIUrl":"https://doi.org/10.22331/q-2025-04-07-1690","url":null,"abstract":"High-dimensional quantum computing has generated significant interest due to its potential to address scalability and error correction challenges faced by traditional qubit-based systems. This paper investigates the Average Gate Fidelity (AGF) of single qudit systems under Markovian noise in the Lindblad formalism, extending previous work by developing a comprehensive theoretical framework for the calculation of higher-order correction terms. We derive general expressions for the perturbative expansion of the Average Gate Infidelity (AGI) in terms of the environmental coupling coefficient and validate these with extensive numerical simulations, emphasizing the transition from linear to nonlinear behaviour in the strong coupling regime. Our findings highlight the dependence of AGI on qudit dimensionality, quantum gate choice, and noise strength, providing critical insights for optimising quantum gate design and error correction protocols. Additionally, we utilise our framework to identify universal bounds for the AGI in the strong coupling regime and explore the practical implications for enhancing the performance of near-term qudit architectures. This study offers a robust foundation for future research and development in high-dimensional quantum computing, contributing to the advancement of robust, high-fidelity quantum operations.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"95 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143789529","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 Edge Detection 量子边缘检测

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-03 DOI: 10.22331/q-2025-04-03-1687

Santiago Llorens, Walther González, Gael Sentís, John Calsamiglia, Ramon Muñoz-Tapia, Emili Bagan

引用次数: 0