检索结果-内蒙古大学图书馆

Role of the extended Hilbert space in the attainability of the quantum Cramér–Rao bound for multiparameter estimation

学校读者我要写书评

暂无评论

arXiv 2024年

作者： Conlon, Lorcán O. Suzuki, Jun Lam, Ping Koy Assad, Syed M. 2 Fusionopolis Way 08-03 Innovis 138634 Singapore Graduate School of Informatics and Engineering The University of Electro-Communications Tokyo182-8585 Japan Centre for Quantum Computation and Communication Technology Department of Quantum Science Australian National University ACT Canberra2601 Australia

The symmetric logarithmic derivative Cramér–Rao bound (SLDCRB) provides a fundamental limit to the minimum variance with which a set of unknown parameters can be estimated in an unbiased manner. It is known that the SLDCRB can be saturated provided the optimal measurements for the individual parameters commute with one another. However, when this is not the case the SLDCRB cannot be attained in general. In the experimentally relevant setting, where quantum states are measured individually, necessary and sufficient conditions for when the SLDCRB can be saturated are not known. In this setting the SLDCRB is attainable provided the SLD operators can be chosen to commute on an extended Hilbert space. However, beyond this relatively little is known about when the SLD operators can be chosen in this manner. In this paper we present explicit examples which demonstrate novel aspects of this condition. Our examples demonstrate that the SLD operators commuting on any two of the following three spaces: support space, support-kernel space and kernel space, is neither a necessary nor sufficient condition for commutativity on the extended space. We present a simple analytic example showing that the Nagaoka–Hayashi Cramér-Rao bound is not always attainable. Finally, we provide necessary and sufficient conditions for the attainability of the SLDCRB in the case when the kernel space is one-dimensional. These results provide new information on the necessary and sufficient conditions for the attainability of the SLDCRB. Copyright © 2024, The Authors. All rights reserved.

关键词： Vector spaces

Coherently mitigating boson samplers with stochastic errors

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Singh, Deepesh Marshman, Ryan J. Walk, Nathan Eisert, Jens Ralph, Timothy C. Lund, Austin P. Centre for Quantum Computation and Communications Technology School of Mathematics and Physics The University of Queensland BrisbaneQLD4072 Australia Dahlem Center for Complex Quantum Systems Freie Universität Berlin Berlin14195 Germany Helmholtz-Zentrum Berlin für Materialien und Energie Berlin14109 Germany

Sampling experiments provide a viable route to show quantum advantages of quantum devices over classical computers in well-defined computational tasks. However, quantum devices such as boson samplers are susceptible to various errors, including stochastic errors due to fabrication imperfections. These cause the implemented unitary operations to deviate randomly from their intended targets, following distributions with finite variance. Whilst full-scale quantum error correction remains challenging in the near term, quantum error mitigation schemes have been devised to estimate expectation values, but it is unclear how these schemes would work for sampling experiments. In this work, we demonstrate that, given access to multiple stochastic unitaries, it is possible to mitigate the effect of these errors in sampling experiments. We adopt the unitary averaging protocol which employs multiple stochastic boson samplers to generate a distribution that approximates the ideal boson sampler distribution as the number of samplers increases. We derive a rigorous upper bound on the trace distance between the output probability distributions induced by invertible vacuum-heralded networks based on the Schur-Weyl duality. This result can be seen concretely as an error mitigation scheme in sampling experiments against stochastic errors. On a broader level, it suggests a path towards understanding error mitigation for sampling experiments and developing analysis tools for photonic circuits incorporating measurements and feed-forward. We further provide other applications of unitary averaging, including its use in implementing the linear combination of unitaries and benchmarking fabrication repeatability in linear optics. Copyright © 2025, The Authors. All rights reserved.

关键词： Distribution functions

Holevo Cramér-Rao bound: How close can we get without entangling measurements?

学校读者我要写书评

暂无评论

arXiv 2024年

作者： Das, Aritra Conlon, Lorcán O. Suzuki, Jun Yung, Simon K. Lam, Ping K. Assad, Syed M. Centre for Quantum Computation and Communication Technology Department of Quantum Science and Technology Australian National University CanberraACT2601 Australia 2 Fusionopolis Way 08-03 Innovis 138634 Singapore Graduate School of Informatics and Engineering The University of Electro-Communications Chofu-shi 1-5-1 Chofugaoka Tokyo182-8585 Japan

In multi-parameter quantum metrology, the resource of entanglement can lead to an increase in efficiency of the estimation process. Entanglement can be used in the state preparation stage, or the measurement stage, or both, to harness this advantage—here we focus on the role of entangling measurements. Specifically, entangling or collective measurements over multiple identical copies of a probe state are known to be superior to measuring each probe individually, but the extent of this improvement is an open problem. It is also known that such entangling measurements, though resource-intensive, are required to attain the ultimate limits in multi-parameter quantum metrology and quantum information processing tasks. In this work we investigate the maximum precision improvement that collective quantum measurements can offer over individual measurements for estimating parameters of qudit states, calling this the ‘collective quantum enhancement’. We show that, whereas the maximum enhancement can, in principle, be a factor of n for estimating n parameters, this bound is not tight for large n. Instead, our results prove an enhancement linear in dimension of the qudit is possible using collective measurements and lead us to conjecture that this is the maximum collective quantum enhancement in any local estimation scenario. Copyright © 2024, The Authors. All rights reserved.

关键词： Probes

Initialization protocol for efficient quantum memories using resolved hyperfine structure

学校读者我要写书评

暂无评论

Physical Review Research 2021年第3期3卷 L032054-L032054页

作者： James S. Stuart Morgan Hedges Rose Ahlefeldt Matthew Sellars Centre for Quantum Computation and Communications Technology Research School of Physics Australian National University Canberra ACT Australia

We describe a quantum memory spectral preparation strategy that optimizes memory efficiency and bandwidth in materials such as Er3+167:Y2SiO5 in a high-field regime, where the hyperfine structure is resolved. We demonstrate the method in Er3+167:Y2SiO5 by preparing spectrally isolated 18-dB-absorbing features on a <1 dB background. Using these features we create an atomic frequency comb and show a quantum storage of 200-ns pulses with 22% efficiency, limited by the background absorption which arises from laser instability. We describe the experimental improvements needed to reach the material limits: O(1)-s spin-state storage, O(100)MHz bandwidth, and >90% efficiency.

关键词： Coherent control Fine & hyperfine structure Optical quantum information processing quantum memories quantum networks quantum repeaters Optical fibers Rare-earth doped crystals

Homodyne measurement with a Schrödinger cat state as a local oscillator

学校读者我要写书评

暂无评论

Physical Review A 2022年第6期106卷 063706-063706页

作者： Joshua Combes Austin P. Lund Department of Electrical Computer and Energy Engineering University of Colorado Boulder Colorado 80309 USA Dahlem Center for Complex Quantum Systems Freie Universität Berlin 14195 Berlin Germany Centre for Quantum Computation and Communications Technology School of Mathematics and Physics The University of Queensland St Lucia QLD Australia

Homodyne measurements are a widely used quantum measurement. Using a coherent state of large amplitude as the local oscillator, it can be shown that the quantum homodyne measurement limits to a field quadrature measurement. In this work, we give an example of a general idea: injecting nonclassical states as a local oscillator can lead to nonclassical measurements. Specifically, we consider injecting a superposition of coherent states, a Schrödinger cat state, as a local oscillator. We derive the Kraus operators and the positive operator-valued measure in this situation.

关键词： Optics & lasers quantum engineering quantum optics quantum sensing

Efficient computation of the Nagaoka-Hayashi bound for multi-parameter estimation with separable measurements

学校读者我要写书评

暂无评论

Efficient computation of the Nagaoka-Hayashi bound for multi...

Conference on quantum Information and Measurement, ICQI 2021

作者： Conlon, Lorcán O. Suzuki, Jun Lam, Ping Koy Assad, Syed M. Centre for Quantum Computation and Communication Technology Department of Quantum Science Australian National University CanberraACT2601 Australia Graduate School of Informatics and Engineering The University of Electro-Communications Tokyo182-8585 Japan School of Physical and Mathematical Sciences Nanyang Technological University Singapore639673 Singapore

We introduce a tight bound for quantum metrology for estimating multiple parameters simultaneously when performing separable measurements;relevant for experimental accessibility. We show that this bound can be efficie... 详细信息

ISBN: (纸本)9781957171012

关键词： Parameter estimation

Initialisation protocol for efficient quantum memories using resolved hyperfine structure

学校读者我要写书评

暂无评论

arXiv 2021年

作者： Stuart, James Hedges, Morgan Ahlefeldt, Rose Sellars, Matthew Centre for Quantum Computation and Communications Technology Research School of Physics Australian National University CanberraACT Australia

We describe a quantum memory spectral preparation strategy that optimises memory efficiency and bandwidth in materials such as 167Er3+:Y2SiO5in a high field regime, where the hyperfine structure is resolved. We demonstrate the method in 167Er3+:Y2SiO5by preparing spectrally isolated 18 dB-absorbing features on a 90% efficiency. © 2021, CC BY.

关键词： Bandwidth

The gap persistence theorem for quantum multiparameter estimation

学校读者我要写书评

暂无评论

arXiv 2022年

One key aspect of quantum metrology, measurement incompatibility, is evident only through the simultaneous estimation of multiple parameters. The symmetric logarithmic derivative Cramér-Rao bound (SLDCRB), gives the attainable precision, if the optimal measurements for estimating each individual parameter commute with one another. As such, when the optimal measurements do not commute, the SLDCRB is not necessarily attainable. In this regard, the Holevo Cramér-Rao bound (HCRB) plays a fundamental role, providing the ultimate attainable precisions when one allows simultaneous measurements on infinitely many copies of a quantum state. For practical purposes, the Nagaoka Cramér-Rao bound (NCRB) is more relevant, applying when restricted to measuring quantum states individually. The interplay between these three bounds dictates how rapidly the ultimate metrological precisions can be approached through collective measurements on finite copies of the probe state. In this work we investigate this interplay. We first consider two parameter estimation and prove that if the HCRB cannot be saturated with a single copy of the probe state, then it cannot be saturated for any finite number of copies of the probe state. As an application of this result, we show that it is impossible to saturate the HCRB for several physically motivated problems, including the simultaneous estimation of phase and phase diffusion. For estimating any number of parameters, we provide necessary and sufficient conditions for the attainability of the SLDCRB with separable measurements. We further prove that if the SLDCRB cannot be reached with a single copy of the probe state, it cannot be reached with collective measurements on any finite number of copies of the probe state. These results together provide necessary and sufficient conditions for the attainability of the SLDCRB for any finite number of copies of the probe state. This solves a significant generalisation of one of the five problems recently

关键词： Probes

Optical cluster-state generation with unitary averaging

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Singh, Deepesh Lund, Austin P. Rohde, Peter P. Centre for Quantum Computation and Communications Technology School of Mathematics and Physics The University of Queensland Australia Dahlem Center for Complex Quantum Systems Freie Universität Berlin Berlin14195 Germany University of Technology Sydney Australia Hearne Institute for Theoretical Physics Department of Physics & Astronomy Louisiana State University United States

Cluster states are the essential resource used in the implementation of Fusion-based quantum computation (FBQC). We introduce a method to generate high-fidelity optical cluster states by utilising the concept of unitary averaging. This error averaging technique is entirely passive and can be readily incorporated into the proposed Psiquantum’s FBQC architecture. Using postselection and the redundant encoding of Fusion gates, we observe an enhancement in the average fidelity of the output cluster state. We also show an improvement in the linear optical Bell-state measurement (BSM) success probability when the BSM is imperfect. Copyright © 2022, The Authors. All rights reserved.

关键词： quantum computers