IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-28 DOI: 10.22331/q-2025-05-28-1755

Hidetaka Manabe, Yuichi Sano

引用次数: 0

Renormalisation of Quantum Cellular Automata 量子元胞自动机的重整化

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-28 DOI: 10.22331/q-2025-05-28-1756

Lorenzo Siro Trezzini, Alessandro Bisio, Paolo Perinotti

引用次数: 0

Operational verification of the existence of a spacetime manifold 时空流形存在的操作验证

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-22 DOI: 10.22331/q-2025-05-22-1753

Nikola Paunkovic, Marko Vojinovic

引用次数: 0

Protecting information in a parametrically driven hybrid quantum system 参数驱动混合量子系统中的信息保护

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-22 DOI: 10.22331/q-2025-05-22-1754

Siddharth Tiwary, Harsh Sharma, Himadri Shekhar Dhar

引用次数: 0

Rise of conditionally clean ancillae for efficient quantum circuit constructions 高效量子电路结构的条件清洁辅助装置的兴起

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-21 DOI: 10.22331/q-2025-05-21-1752

Tanuj Khattar, Craig Gidney

{"title":"Rise of conditionally clean ancillae for efficient quantum circuit constructions","authors":"Tanuj Khattar, Craig Gidney","doi":"10.22331/q-2025-05-21-1752","DOIUrl":"https://doi.org/10.22331/q-2025-05-21-1752","url":null,"abstract":"We introduce conditionally clean ancilla qubits, a new quantum resource, recently explored by [17], that bridges the gap between traditional clean and dirty ancillae. Like dirty ancillae, they begin and end in an unknown state and can be borrowed from existing system qubits, avoiding the space overhead of explicit qubit allocation. Like clean ancillae, they can be treated as initialized in a known state within specific computations, thus avoiding the overhead of toggle detection required for dirty ancillae. We present new circuit constructions leveraging conditionally clean ancillae to achieve lower gate counts and depths, particularly with limited ancilla availability. Specifically, we provide constructions for: \u0000 (a) $n$-controlled NOT using $2n$ Toffolis and $O(log{n})$ depth given 2 clean ancillae. (b) $n$-qubit incrementer using $3n$ Toffolis given $log_2^*{n}$ clean ancillae. (c) $n$-qubit quantum-classical comparator using $3n$ Toffolis given $log_2^*{n}$ clean ancillae. (d) unary iteration over $[0,N)$ using $2.5N$ Toffolis given $log_2^*{n}$ clean ancillae. (e) unary iteration via skew tree over $[0, N)$ using $1.25N$ Toffolis given $n$ dirty ancillae. \u0000 We also introduce $textit{laddered toggle detection}$, a technique to replace clean ancillae with dirty ancillae in all our constructions, incurring a 2x Toffoli gate overhead. Our results demonstrate that conditionally clean ancillae are a valuable tool for quantum circuit design, especially in the resource-constrained early fault-tolerant era.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"19 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144104723","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

Classical Benchmarks for Variational Quantum Eigensolver Simulations of the Hubbard Model 哈伯德模型变分量子特征解算器模拟的经典基准

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-20 DOI: 10.22331/q-2025-05-20-1748

Antonios M. Alvertis, Abid Khan, Thomas Iadecola, Peter P. Orth, Norm Tubman

{"title":"Classical Benchmarks for Variational Quantum Eigensolver Simulations of the Hubbard Model","authors":"Antonios M. Alvertis, Abid Khan, Thomas Iadecola, Peter P. Orth, Norm Tubman","doi":"10.22331/q-2025-05-20-1748","DOIUrl":"https://doi.org/10.22331/q-2025-05-20-1748","url":null,"abstract":"Simulating the Hubbard model is of great interest to a wide range of applications within condensed matter physics, however its solution on classical computers remains challenging in dimensions larger than one. The relative simplicity of this model, embodied by the sparseness of the Hamiltonian matrix, allows for its efficient implementation on quantum computers, and for its approximate solution using variational algorithms such as the variational quantum eigensolver. While these algorithms have been shown to reproduce the qualitative features of the Hubbard model, their quantitative accuracy in terms of producing true ground state energies and other properties, and the dependence of this accuracy on the system size and interaction strength, the choice of variational ansatz, and the degree of spatial inhomogeneity in the model, remains unknown. Here we present a rigorous classical benchmarking study, demonstrating the potential impact of these factors on the accuracy of the variational solution of the Hubbard model on quantum hardware, for systems with up to $32$ qubits. We find that even when using the most accurate wavefunction ansÃ¤tze for the Hubbard model, the error in its ground state energy and wavefunction plateaus for larger lattices, while stronger electronic correlations magnify this issue. Concurrently, spatially inhomogeneous parameters and the presence of off-site Coulomb interactions only have a small effect on the accuracy of the computed ground state energies. Our study highlights the capabilities and limitations of current approaches for solving the Hubbard model on quantum hardware, and we discuss potential future avenues of research.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"73 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144097665","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

Transfer and routing of Gaussian states through quantum complex networks with and without community structure 具有和不具有社团结构的量子复杂网络中高斯态的传输和路由

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-20 DOI: 10.22331/q-2025-05-20-1751

Markku Hahto, Johannes Nokkala, Guillermo García-Pérez, Sabrina Maniscalco, Jyrki Piilo

{"title":"Transfer and routing of Gaussian states through quantum complex networks with and without community structure","authors":"Markku Hahto, Johannes Nokkala, Guillermo García-Pérez, Sabrina Maniscalco, Jyrki Piilo","doi":"10.22331/q-2025-05-20-1751","DOIUrl":"https://doi.org/10.22331/q-2025-05-20-1751","url":null,"abstract":"The goal in quantum state transfer is to avoid the need to physically transport carriers of quantum information. This is achieved by using a suitably engineered Hamiltonian that induces the transfer of the state of one subsystem to another. A less known generalization of state transfer considers multiple systems such that any pair can exchange quantum information and transfers can take place at any time, starting and stopping independently. This is sometimes called routing of quantum states. State transfer in particular has received a great deal of attention, however the vast majority of results in both state transfer and routing concern qubits transferred in a network of restricted structure. Here we consider routing of single-mode Gaussian states and entanglement through complex networks of quantum harmonic oscillators. We compare a protocol where the transfer is completed in a single step but the effective Hamiltonian only approximately transfers the state with one where the transfer can in principle be perfect but the transfer is done in two steps, and also illustrate the state-dependency of the transfer fidelity. We find that even in a random and homogeneous network, the transfer fidelity still depends on the degree of the nodes for any link density, and that in both random and complex networks it is the community structure that controls the appearance of higher frequency normal modes useful for transfer. Finally, we find that networks of sufficient complexity may have superior routing performance over superficially similar random networks. Our results pave the way for further exploration of the role of community structure in state transfer and related tasks.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"35 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144104722","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

Universal adjointation of isometry operations using conversion of quantum supermaps 利用量子超映射转换的等距运算的普遍自洽

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-20 DOI: 10.22331/q-2025-05-20-1750

Satoshi Yoshida, Akihito Soeda, Mio Murao

{"title":"Universal adjointation of isometry operations using conversion of quantum supermaps","authors":"Satoshi Yoshida, Akihito Soeda, Mio Murao","doi":"10.22331/q-2025-05-20-1750","DOIUrl":"https://doi.org/10.22331/q-2025-05-20-1750","url":null,"abstract":"Identification of possible transformations of quantum objects including quantum states and quantum operations is indispensable in developing quantum algorithms. Universal transformations, defined as input-independent transformations, appear in various quantum applications. Such is the case for universal transformations of unitary operations. However, extending these transformations to non-unitary operations is nontrivial and largely unresolved. Addressing this, we introduce $textit{isometry adjointation}$ protocols that transform an input isometry operation into its adjoint operation, which include both unitary operation and quantum state transformations. The paper details the construction of parallel and sequential isometry adjointation protocols, derived from unitary inversion protocols using quantum combs and the (dual) Clebsch-Gordan transforms, and achieving optimal approximation error. This error is shown to be independent of the output dimension of the isometry operation. In particular, we explicitly obtain an asymptotically optimal parallel protocol achieving an approximation error $epsilon = Theta(d^2/n)$, where $d$ is the input dimension of the isometry operation and $n$ is the number of calls of the isometry operation. The research also extends to isometry inversion and universal error detection, employing semidefinite programming to assess optimal performances. The findings suggest that the optimal performance of general protocols in isometry adjointation and universal error detection is not dependent on the output dimension, and that indefinite causal order protocols offer advantages over sequential ones in isometry inversion and universal error detection.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"35 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144104734","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

The measurement postulates of quantum mechanics are not redundant 量子力学的测量假设不是多余的

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-20 DOI: 10.22331/q-2025-05-20-1749

Adrian Kent

{"title":"The measurement postulates of quantum mechanics are not redundant","authors":"Adrian Kent","doi":"10.22331/q-2025-05-20-1749","DOIUrl":"https://doi.org/10.22331/q-2025-05-20-1749","url":null,"abstract":"Masanes, Galley and Müller [39] argue that the measurement postulates of non-relativistic quantum mechanics follow from the structural postulates together with an assumption they call the \"possibility of state estimation\". Their argument also relies on what they term a \"theory-independent characterization of measurements for single and multipartite systems\". We refute their conclusion, giving explicit examples of non-quantum measurement and state update rules that satisfy all their assumptions. We also show that their \"possibility of state estimation\" assumption is neither necessary nor sufficient to ensure a sensible notion of state estimation within a theory whose states are described by the quantum formalism. We further show their purportedly \"theory-independent\" characterization assumes several properties of quantum measurements that exclude plausible alternative types of measurement. We illustrate all these points with specific alternative measurement postulates and post-measurement state update rules. We conclude that, contrary to some folklore, quantum mechanics is by no means an island in theory-space. It can consistently be extended by rules for obtaining information about quantum states other than via POVMs. Whether such rules are realised in nature, for example in linking quantum theory and gravity, is an empirical question that cannot be resolved by theoretical analysis alone.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"2 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144097664","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

Trainability and Expressivity of Hamming-Weight Preserving Quantum Circuits for Machine Learning 用于机器学习的哈明-保权量子电路的可训练性和表达性

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-05-15 DOI: 10.22331/q-2025-05-15-1745

Léo Monbroussou, Eliott Z. Mamon, Jonas Landman, Alex B. Grilo, Romain Kukla, Elham Kashefi

{"title":"Trainability and Expressivity of Hamming-Weight Preserving Quantum Circuits for Machine Learning","authors":"Léo Monbroussou, Eliott Z. Mamon, Jonas Landman, Alex B. Grilo, Romain Kukla, Elham Kashefi","doi":"10.22331/q-2025-05-15-1745","DOIUrl":"https://doi.org/10.22331/q-2025-05-15-1745","url":null,"abstract":"Quantum machine learning (QML) has become a promising area for real world applications of quantum computers, but near-term methods and their scalability are still important research topics. In this context, we analyze the trainability and controllability of specific Hamming weight preserving variational quantum circuits (VQCs). These circuits use qubit gates that preserve subspaces of the Hilbert space, spanned by basis states with fixed Hamming weight $k$. In this work, we first design and prove the feasibility of new heuristic data loaders, performing quantum amplitude encoding of $binom{n}{k}$-dimensional vectors by training an $n$-qubit quantum circuit. These data loaders are obtained using controllability arguments, by checking the Quantum Fisher Information Matrix (QFIM)'s rank. Second, we provide a theoretical justification for the fact that the rank of the QFIM of any VQC state is almost-everywhere constant, which is of separate interest. Lastly, we analyze the trainability of Hamming weight preserving circuits, and show that the variance of the $l_2$ cost function gradient is bounded according to the dimension $binom{n}{k}$ of the subspace. This proves conditions of existence/lack of Barren Plateaus for these circuits, and highlights a setting where a recent conjecture on the link between controllability and trainability of variational quantum circuits does not apply.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"96 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144066455","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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