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A purification scheme which utilizes the action of repeated measurements on a (part of a total) quantum system is briefly reviewed and is applied to a few simple systems to show how it enables us to extract an entangled state as a target…

Quantum Physics · Physics 2007-05-23 Hiromichi Nakazato , Makoto Unoki , Kazuya Yuasa

A multi-slit interference experiment, with which-way detectors, in the presence of environment induced decoherence, is theoretically analyzed. The effect of environment is modeled via a coupling to a bath of harmonic oscillators. Through an…

Quantum Physics · Physics 2018-11-02 Anu Venugopalan , Sandeep Mishra , Tabish Qureshi

Many quantum algorithms, including recently proposed hybrid classical/quantum algorithms, make use of restricted tomography of the quantum state that measures the reduced density matrices, or marginals, of the full state. The most…

Quantum Physics · Physics 2018-05-16 Nicholas C. Rubin , Ryan Babbush , Jarrod McClean

Decoherence is widely felt to have something to do with the quantum measurement problem, but getting clear on just what is made difficult by the fact that the "measurement problem", as traditionally presented in foundational and…

Quantum Physics · Physics 2015-06-03 David Wallace

Purification is a process in which decoherence is partially reversed by using several input systems which have been subject to the same noise. The purity of the outputs generally increases with the number of input systems, and decreases…

Quantum Physics · Physics 2007-05-23 M. Keyl , R. F. Werner

Decoherence and dissipation in quantum systems has been studied extensively in the context of Quantum Brownian Motion. Effective decoherence in coarse grained quantum systems has been a central issue in recent efforts by Zurek and by Hartle…

High Energy Physics - Theory · Physics 2007-05-23 Michael R. Gallis

Randomized measurements are useful for analyzing quantum systems especially when quantum control is not fully perfect. However, their practical realization typically requires multiple rotations in the complex space due to the adoption of…

Quantum Physics · Physics 2025-08-28 Jin-Min Liang , Satoya Imai , Shuheng Liu , Shao-Ming Fei , Otfried Gühne , Qiongyi He

Macroscopic behavior such as the lack of interference patterns has been attributed to "decoherence", a word with several possible definitions such as (1) the loss of off-diagonal density matrix elements, (2) the flow of information to the…

Quantum Physics · Physics 2015-05-30 Patrick J. Coles

Open quantum systems are governed by both unitary and non-unitary dynamics, with dissipation arising from the latter. Traditional quantum divergence measures, such as quantum relative entropy, fail to account for the non-unitary oriented…

Quantum Physics · Physics 2025-09-23 Tomohiro Nishiyama , Yoshihiko Hasegawa

We investigate the issue of assisted coherence distillation in the asymptotic limit (considering infinite copies of the resource states), by coordinately performing the identical local operations on the auxiliary systems of each copy. When…

Quantum Physics · Physics 2022-08-24 Huang-Qiu-Chen Wang , Qi Luo , Qi-Ping Su , Yong-Nan Sun , Nengji Zhou , Li Yu , Zhe Sun

Quantum metrology offers an enhanced performance in experiments such as gravitational wave-detection, magnetometry or atomic clocks frequency calibration. The enhancement, however, requires a delicate tuning of relevant quantum features…

Quantum Physics · Physics 2013-07-25 Jan Kolodynski , Rafal Demkowicz-Dobrzanski

In [J. C. Howell and J. A. Yeazell, Phys. Rev. A 62, 012102 (2000)], a proposal is made to generate entangled macroscopically distinguishable states of two spatially separated traveling optical modes. We model the decoherence due to light…

Quantum Physics · Physics 2016-04-26 J. Clausen , L. Knoell , D. -G. Welsch

The distribution of entangled states of light over long distances is a major challenge in the field of quantum information. Optical losses, phase diffusion and mixing with thermal states lead to decoherence and destroy the non-classical…

We present efficient and practical protocols to measure the second R\'enyi entropy (RE), whose exponential is known as the purity. We achieve this by establishing a direct connection to a Loschmidt echo (LE) type measurement sequence,…

Quantum Physics · Physics 2026-02-12 Yi-Neng Zhou , Robin Löwenberg , Julian Sonner

Quantum coherence, a basic feature of quantum mechanics residing in superpositions of quantum states, is a resource for quantum information processing. Coherence emerges in a fundamentally different way for nonidentical and identical…

Quantifying intrinsic irreversibility in open quantum dynamics is central to understanding decoherence and information loss in many-body systems. In this work, we introduce the Choi echo, which provides an operational interpretation of the…

Quantum Physics · Physics 2025-12-15 Jose Alfredo de Leon , Miguel Gonzalez , Carlos Diaz-Mejia

In this work we investigate the relation between quantum measurements and decoherence, in order to formally express the necessity of the latter for obtaining an informative output from the former. To this aim, referring to the Von Neumann…

Quantum Physics · Physics 2015-06-23 Pietro Liuzzo-Scorpo , Alessandro Cuccoli , Paola Verrucchi

We consider the thermal aspect of a system composed of two coupled harmonic oscillators and study the corresponding purity. We initially consider a situation where the system is brought to a canonical thermal equilibrium with a heat-bath at…

Quantum Physics · Physics 2018-09-26 Abdeldjalil Merdaci , Ahmed Jellal , Ayman Al Sawalha , Abdelhadi Bahaoui

The destruction of quantum-mechanical phase coherence by a fluctuating quantum bath has been investigated mostly for a single particle. However, for electronic transport through disordered samples and mesoscopic interference setups, we have…

Mesoscale and Nanoscale Physics · Physics 2015-06-25 Florian Marquardt

Measurement is one of the key concepts which discriminates classical and quantum physics. Unlike classical systems, a measurement on a quantum system typically alters it drastically as a result of wave function collapse. Here we suggest…

Quantum Physics · Physics 2018-07-18 Abolfazl Bayat , Bedoor Alkurtass , Pasquale Sodano , Henrik Johannesson , Sougato Bose