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The quantum variables that can be accessed directly by experiments are described by observables. Therefore, physical parameters can only be evaluated indirectly, via estimations based on experimental measurement results. I show that the…

Quantum Physics · Physics 2012-12-12 B. M. Escher

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…

The detection of entanglement provides a definitive proof of quantumness. Its ascertainment might be challenging for hot or macroscopic objects, where entanglement is typically weak, but nevertheless present. Here we propose a platform for…

Quantum Physics · Physics 2023-05-10 Tanjung Krisnanda , Tomasz Paterek , Mauro Paternostro , Timothy C. H. Liew

Recent advancements in quantum computing (QC) and machine learning (ML) have garnered significant attention, leading to substantial efforts toward the development of quantum machine learning (QML) algorithms to address a variety of complex…

Quantum Physics · Physics 2024-12-18 Samuel Yen-Chi Chen

Quantum technologies work by utilizing properties inherent in quantum systems such as quantum coherence and quantum entanglement and are expected to be superior to classical counterparts for solving certain problems in science and…

Quantum Physics · Physics 2023-04-10 Yusuke Hama , Hirofumi Nishi

We introduce a novel protocol, which enables Heisenberg-limited quantum-enhanced sensing using the dynamics of any interacting many-body Hamiltonian. Our approach - dubbed butterfly metrology - utilizes a single application of forward and…

Quantum sensors leverage nonclassical resources to achieve sensing precision at the Heisenberg limit, surpassing the standard quantum limit attainable through classical strategies. However, a critical issue is that the environmental noise…

Quantum Physics · Physics 2025-11-24 Hang Xu , Tailong Xiao , Jingzheng Huang , Jianping Fan , Guihua Zeng

We analyze quantum metrological protocols, where the sensing system is linearly coupled to a bosonic environment, by performing a Markovian embedding of the problem based on pseudomode formalism. This allows us to effectively model the…

Quantum Physics · Physics 2026-02-13 Arpan Das , Rafał Demkowicz-Dobrzański

Characterization of quantum systems from experimental data is a central problem in quantum science and technology. But which measurements should be used to gather data in the first place? While optimal measurement choices can be worked out…

Quantum Physics · Physics 2025-07-15 Jiaxin Huang , Yan Zhu , Giulio Chiribella , Ya-Dong Wu

A one-dimensional quantum oscillator is monitored by taking repeated position measurements. As a first con- tribution, it is shown that, under a quantum nondemolition measurement scheme applied to a system initially at the ground state, (i)…

Quantum Physics · Physics 2015-11-13 Vincenzo Matta , Vincenzo Pierro

Quantum machine learning is an approach that aims to improve the performance of machine learning methods by leveraging the properties of quantum computers. In quantum circuit learning (QCL), a supervised learning method that can be…

We study an electrostatic qubit monitored by a point-contact detector. Projecting an entire qubit-detector wave function on the detector eigenstates we determine the precision limit for the qubit measurements, allowed by quantum mechanics.…

Quantum Physics · Physics 2009-11-11 S. A. Gurvitz

In the last years several estimation strategies have been formulated to determine the value of an unknown parameter in the most precise way, taking into account the presence of noise. These strategies typically rely on the use of quantum…

Quantum Physics · Physics 2021-08-31 Andrea Smirne , Andreas Lemmer , Martin B. Plenio , Susana F. Huelga

We present a general framework for sensitivity optimization in quantum parameter estimation schemes based on continuous (indirect) observation of a dynamical system. As an illustrative example, we analyze the canonical scenario of…

Quantum Physics · Physics 2009-11-07 F. Verstraete , A. C. Doherty , H. Mabuchi

During their operation, due to shifts in environmental conditions, devices undergo various forms of detuning from their optimal settings. Typically, this is addressed through control loops, which monitor variables and the device…

Quantum Physics · Physics 2024-04-17 T. Crosta , L. Rebón , F. Vilariño , J. M. Matera , M. Bilkis

Quantum errors in noisy environments remain a major obstacle to advancing quantum information technology. In this work, we expand a recently developed geometric framework, originally utilized for analyzing noise accumulation and creating…

Quantum Physics · Physics 2024-07-11 Junkai Zeng , Yong-Ju Hai , Hao Liang , Xiu-Hao Deng

Quantum metrology and quantum communications are typically considered as distinct applications in the broader portfolio of quantum technologies. However, there are cases where we might want to combine the two and recent proposals have shown…

Quantum Physics · Physics 2023-02-08 Sean William Moore , Jacob Andrew Dunningham

We consider a quantum sensor network of qubit sensors coupled to a field $f(\vec{x};\vec{\theta})$ analytically parameterized by the vector of parameters $\vec\theta$. The qubit sensors are fixed at positions $\vec{x}_1,\dots,\vec{x}_d$.…

Quantum Physics · Physics 2021-04-07 Timothy Qian , Jacob Bringewatt , Igor Boettcher , Przemyslaw Bienias , Alexey V. Gorshkov

In quantum metrology, entangled states of many-particle systems are investigated to enhance measurement precision of the most precise clocks and field sensors. While single-parameter quantum metrology is well established, many metrological…

We present a dynamic learning paradigm for "programming" a general quantum computer. A learning algorithm is used to find the control parameters for a coupled qubit system, such that the system at an initial time evolves to a state in which…

Quantum Physics · Physics 2008-08-12 E. C. Behrman , J. E. Steck , P. Kumar , K. A. Walsh