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Entropy 2018, 20(1), 39; https://doi.org/10.3390/e20010039

Robust Macroscopic Quantum Measurements in the Presence of Limited Control and Knowledge

Department of Applied Physics, University of Geneva, 1211 Geneva 4, Switzerland
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Received: 31 October 2017 / Revised: 8 December 2017 / Accepted: 26 December 2017 / Published: 9 January 2018
(This article belongs to the Special Issue Quantum Information and Foundations)
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Abstract

Quantum measurements have intrinsic properties that seem incompatible with our everyday-life macroscopic measurements. Macroscopic Quantum Measurement (MQM) is a concept that aims at bridging the gap between well-understood microscopic quantum measurements and macroscopic classical measurements. In this paper, we focus on the task of the polarization direction estimation of a system of N spins 1/2 particles and investigate the model some of us proposed in Barnea et al., 2017. This model is based on a von Neumann pointer measurement, where each spin component of the system is coupled to one of the three spatial component directions of a pointer. It shows traits of a classical measurement for an intermediate coupling strength. We investigate relaxations of the assumptions on the initial knowledge about the state and on the control over the MQM. We show that the model is robust with regard to these relaxations. It performs well for thermal states and a lack of knowledge about the size of the system. Furthermore, a lack of control on the MQM can be compensated by repeated “ultra-weak” measurements. View Full-Text
Keywords: quantum measurement; quantum estimation; macroscopic quantum measurement quantum measurement; quantum estimation; macroscopic quantum measurement
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Renou, M.-O.; Gisin, N.; Fröwis, F. Robust Macroscopic Quantum Measurements in the Presence of Limited Control and Knowledge. Entropy 2018, 20, 39.

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