Quantum最新文献 - Book学术

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

Impact of decoherence on the fidelity of quantum gates leaving the computational subspace

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-03 DOI: 10.22331/q-2025-04-03-1684

Tahereh Abad, Yoni Schattner, Anton Frisk Kockum, Göran Johansson

引用次数: 0

Which features of quantum physics are not fundamentally quantum but are due to indeterminism?

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-03 DOI: 10.22331/q-2025-04-03-1686

Flavio Del Santo, Nicolas Gisin

引用次数: 0

Learning in Quantum Common-Interest Games and the Separability Problem 量子共同利益博弈中的学习与可分性问题

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-03 DOI: 10.22331/q-2025-04-03-1689

Wayne Lin, Georgios Piliouras, Ryann Sim, Antonios Varvitsiotis

{"title":"Learning in Quantum Common-Interest Games and the Separability Problem","authors":"Wayne Lin, Georgios Piliouras, Ryann Sim, Antonios Varvitsiotis","doi":"10.22331/q-2025-04-03-1689","DOIUrl":"https://doi.org/10.22331/q-2025-04-03-1689","url":null,"abstract":"Learning in games has emerged as a powerful tool for machine learning with numerous applications. Quantum games model interactions between strategic players who have access to quantum resources, and several recent works have studied learning in the competitive regime of quantum zero-sum games. Going beyond this setting, we introduce quantum common-interest games (CIGs) where players have density matrices as strategies and their interests are perfectly aligned. We bridge the gap between optimization and game theory by establishing the equivalence between KKT (first-order stationary) points of an instance of the Best Separable State (BSS) problem and the Nash equilibria of its corresponding quantum CIG. This allows learning dynamics for the quantum CIG to be seen as decentralized algorithms for the BSS problem. Taking the perspective of learning in games, we then introduce non-commutative extensions of the continuous-time replicator dynamics and the discrete-time best response dynamics/linear multiplicative weights update for learning in quantum CIGs. We prove analogues of classical convergence results of the dynamics and explore differences which arise in the quantum setting. Finally, we corroborate our theoretical findings through extensive experiments.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"38 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143775663","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

Free fermions under adaptive quantum dynamics 自适应量子动力学下的自由费米子

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-04-03 DOI: 10.22331/q-2025-04-03-1685

Vikram Ravindranath, Zhi-Cheng Yang, Xiao Chen

{"title":"Free fermions under adaptive quantum dynamics","authors":"Vikram Ravindranath, Zhi-Cheng Yang, Xiao Chen","doi":"10.22331/q-2025-04-03-1685","DOIUrl":"https://doi.org/10.22331/q-2025-04-03-1685","url":null,"abstract":"We study free fermion systems under adaptive quantum dynamics consisting of unitary gates and projective measurements followed by corrective unitary operations. We further introduce a classical flag for each site, allowing for an active or inactive status which determines whether or not the unitary gates are allowed to apply. In this dynamics, the individual quantum trajectories exhibit a measurement-induced entanglement transition from critical to area-law scaling above a critical measurement rate, similar to previously studied models of free fermions under continuous monitoring. Furthermore, we find that the corrective unitary operations can steer the system into a state characterized by charge-density-wave order. Consequently, an additional phase transition occurs, which can be observed at both the level of the quantum trajectory and the quantum channel. We establish that the entanglement transition and the steering transition are fundamentally distinct. The latter transition belongs to the parity-conserving (PC) universality class, arising from the interplay between the inherent fermionic parity and classical labelling. We demonstrate both the entanglement and the steering transitions via efficient numerical simulations of free fermion systems, which confirm the PC universality class of the latter.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"73 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143766731","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