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The simultaneous estimation of multiple unknown parameters is the most general scenario in quantum sensing. Quantum multi-parameter estimation theory provides fundamental bounds on the achievable precision of simultaneous estimation.…

Quantum Physics · Physics 2025-12-02 Yaoling Yang , Victor Montenegro , Abolfazl Bayat

How well can multiple incompatible observables be implemented by a single measurement? This is a fundamental problem in quantum mechanics with wide implications for the performance optimization of numerous tasks in quantum information…

Quantum Physics · Physics 2024-10-10 Hongzhen Chen , Lingna Wang , Haidong Yuan

Quantum learning encounters fundamental challenges when estimating non-linear properties, owing to the inherent linearity of quantum mechanics. Although recent advances in single-copy randomized measurement protocols have achieved optimal…

Quantum Physics · Physics 2026-03-30 Zhenyu Du , Yifan Tang , Andreas Elben , Ingo Roth , Jens Eisert , Zhenhuan Liu

Quantum bits, or qubits, are the fundamental building blocks of present quantum computers. Hence, it is important to be able to characterize the state of a qubit as accurately as possible. By evaluating the qubit characterization problem…

Quantum Physics · Physics 2024-02-27 Bacui Li , Lorcan O. Conlon , Ping Koy Lam , Syed M. Assad

We derive a standard quantum limit for probing mechanical energy quantization in a class of systems with mechanical modes parametrically coupled to external degrees of freedom. To resolve a single mechanical quantum, it requires a…

Quantum Physics · Physics 2009-09-11 Haixing Miao , Stefan Danilishin , Thomas Corbitt , Yanbei Chen

An efficient decoder is essential for quantum error correction, and data-driven neural decoders have emerged as promising, flexible solutions. Here, we introduce a diffusion model framework to infer logical errors from syndrome measurements…

Quantum Physics · Physics 2025-09-29 Zejun Liu , Anqi Gong , Bryan K. Clark

Quantum mechanics is sensitive to the geometry of the underlying space. Here, we present a framework for quantum scattering of a non-relativistic particle confined to a two-dimensional space. When the motion manifold hosts localized…

Quantum Physics · Physics 2024-02-19 Lars Meschede , Benjamin Schwager , Dominik Schulz , Jamal Berakdar

High precision measurements are essential to solve major scientific and technological challenges, from gravitational wave detection to healthcare diagnostics. Quantum sensing delivers greater precision, but an in-depth optimisation of…

Quantum-limited estimation of an optical phase using adaptive (i.e. real-time feedback) techniques is reviewed. One case is explored in detail, as it can be understood using only elementary concepts such as photonic shot-noise and error…

Quantum Physics · Physics 2007-05-23 H. M. Wiseman

In this paper, we use the non-linear dynamics of the individual quantum trajectories of an optical cavity inside an instantaneous quantum feedback loop to measure the phase shift between two pathways of light with an accuracy above the…

Quantum Physics · Physics 2016-08-31 Lewis A. Clark , Adam Stokes , Almut Beige

Experimental quantum simulators have become large and complex enough that discovering new physics from the huge amount of measurement data can be quite challenging, especially when little theoretical understanding of the simulated model is…

Quantum Physics · Physics 2020-12-08 Alexander Lidiak , Zhexuan Gong

This paper discusses work developed in recent years, in the domain of quantum optics, which has led to a better understanding of the classical limit of quantum mechanics. New techniques have been proposed, and experimentally demonstrated,…

Quantum Physics · Physics 2015-06-26 Luiz Davidovich

In a noisy environment with weak single levels, quantum illumination can outperform classical illumination in determining the presence and range of a target object even in the limit of sub-optimal measurements based on non-simultaneous,…

Quantum Physics · Physics 2023-08-08 Richard J. Murchie , Jonathan D. Pritchard , John Jeffers

Non-classical correlations in optical beams offer the unprecedented opportunity of surpassing conventional limits of sensitivity and resolution in optical measurements and imaging, especially but not only, when a low photon flux down to the…

Quantum Physics · Physics 2019-04-03 Ivano Ruo-Berchera , Ivo Pietro Degiovanni

Quantum-optimal discrimination between one and two closely separated light sources can be achieved by ideal spatial-mode demultiplexing, simply monitoring whether a photon is detected in a single antisymmetric mode. However, we show that…

Quantum parameter estimation theory is an important component of quantum information theory and provides the statistical foundation that underpins important topics such as quantum system identification and quantum waveform estimation. When…

Quantum Physics · Physics 2024-12-24 Hendra I. Nurdin

Understanding the fundamental limits on the precision to which an optical phase can be estimated is of key interest for many investigative techniques utilized across science and technology. We study the estimation of a fixed optical phase…

Quantum Physics · Physics 2017-12-13 Patrick M. Birchall , Jeremy L. O'Brien , Jonathan C. F. Matthews , Hugo Cable

Photo-detection plays a fundamental role in experimental quantum optics and is of particular importance in the emerging field of linear optics quantum computing. Present theoretical treatment of photo-detectors is highly idealized and fails…

Quantum Physics · Physics 2009-11-11 Peter P. Rohde , Timothy C. Ralph

Quantum imaging with undetected light has recently emerged as a technique in which quantum correlations and nonlinear interferometry are combined to decouple illumination and detection paths. This approach has been more recently extended…

High-quality quantum state generation is essential for advanced quantum information processing, including quantum communication, quantum sensing, and quantum computing. In practice, various error sources degrade the quality of quantum…