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The future development of quantum technologies relies on creating and manipulating quantum systems of increasing complexity, with key applications in computation, simulation and sensing. This poses severe challenges in the efficient…

Quantum trajectories describe the stochastic evolution of an open quantum system conditioned on continuous monitoring of its output, such as by an ideal photodetector. In practice an experimenter has access to an output filtered through…

Quantum Physics · Physics 2016-09-08 P. Warszawski , H. M. Wiseman

Quantum machine learning uses principles from quantum mechanics to process data, offering potential advances in speed and performance. However, previous work has shown that these models are susceptible to attacks that manipulate input data…

A quantum trajectory describes the evolution of a quantum system undergoing indirect measurement. In the discrete-time setting, the state of the system is updated by applying Kraus operators according to the measurement results. From an…

Quantum Physics · Physics 2022-04-04 Maël Bompais , Nina H. Amini , Clément Pellegrini

The report presents a general approach for estimating quantum information technologies by means of fuzzy quantum measurements. The developed methods are used for precision reconstruction of quantum states under conditions of significant…

Quantum Physics · Physics 2022-01-11 Yu. I. Bogdanov

Quantum parameter estimation, the ability to precisely obtain a classical value in a quantum system, is very important to many key quantum technologies. Many of these technologies rely on an optical probe, either coherent or squeezed states…

Quantum Physics · Physics 2015-05-14 Trevor A. Wheatley , Mankei Tsang , Ian R. Petersen , Elanor H. Huntington

Quantum state engineering plays a vital role in various applications in the field of quantum information. Different strategies, including drive-and-dissipation, adiabatic cooling, and measurement-based steering, have been proposed in the…

Quantum Physics · Physics 2024-07-09 E. Medina-Guerra , Parveen Kumar , I. V. Gornyi , Yuval Gefen

Estimation of physical observables for unknown quantum states is an important problem that underlies a wide range of fields, including quantum information processing, quantum physics, and quantum chemistry. In the context of quantum…

Quantum Physics · Physics 2024-05-21 Yuma Nakamura , Yoshichika Yano , Nobuyuki Yoshioka

Here, we are concerned with comparing estimation schemes for the quantum state under continuous measurement (quantum trajectories), namely quantum state filtering and, as introduced by us [Phys. Rev. Lett. 115, 180407 (2015)], quantum state…

Quantum Physics · Physics 2020-11-18 Ivonne Guevara , Howard M. Wiseman

The reliable characterization of quantum states as well as any potential noise in various quantum systems is crucial for advancing quantum technologies. In this work we propose the concept of corrupted sensing quantum state tomography which…

Quantum Physics · Physics 2025-05-07 Mengru Ma , Jiangwei Shang

In this paper, we propose a scheme to eliminate the influence of noises on system dynamics, by means of a sequential unsharp measurements and unitary feedback operations. The unsharp measurements are carried out periodically during system…

Quantum Physics · Physics 2018-09-19 Du Ran , Ye-Hong Chen , Zhi-Cheng Shi , Zhen-Biao Yang , Jie Song , Yan Xia

In quantum physics, measurement results are random but their statistics can be predicted assuming some knowledge about the system in the past. Additional knowledge from a future measurement deeply changes the statistics in the present and…

Measurements are a vital part of any quantum computation, whether as a final step to retrieve results, as an intermediate step to inform subsequent operations, or as part of the computation itself (as in measurement-based quantum…

Quantum Physics · Physics 2023-04-14 Stefanie J. Beale , Joel J. Wallman

In quantum information processing quantum operations are often processed alongside measurements which result in classical data. Due to the information gain of classical measurement outputs non-unitary dynamical processes can take place on…

Quantum measurements are described as instantaneous projections in textbooks. They can be stretched out in time using weak measurements, whereby one can observe the evolution of a quantum state as it heads towards one of the eigenstates of…

Quantum Physics · Physics 2018-04-11 Parveen Kumar , Suman Kundu , Madhavi Chand , R. Vijayaraghavan , Apoorva Patel

The method of restricted path integrals allows one to effectively consider continuous (prolonged in time) measurements of quantum systems. Monitoring of the system coordinates is such a continuous measurement that allows one to describe a…

chao-dyn · Physics 2008-02-03 Michael Mensky

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems…

Quantum measurements affect the state of the observed systems via back-action. While projective measurements extract maximal classical information, they drastically alter the system's configuration. In contrast, indirect measurements…

Quantum Physics · Physics 2026-04-06 Giacomo Franceschetto , Marcin Płodzień , Maciej Lewenstein , Antonio Acín , Pere Mujal

A crucial subroutine for various quantum computing and communication algorithms is to efficiently extract different classical properties of quantum states. In a notable recent theoretical work by Huang, Kueng, and Preskill [Nat. Phys. 16,…

Quantum Physics · Physics 2021-11-19 Ting Zhang , Jinzhao Sun , Xiao-Xu Fang , Xiao-Ming Zhang , Xiao Yuan , He Lu

The dynamics of quantum systems are unavoidably influenced by their environment and in turn observing a quantum system (probe) can allow one to measure its environment: Measurements and controlled manipulation of the probe such as dynamical…

Quantum Physics · Physics 2019-07-16 Matthias M. Müller , Stefano Gherardini , Filippo Caruso