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Quantum Machines: Measurement and Control of Engineered Quantum SystemsLecture Notes of the Les Houches Summer School: Volume 96, July 2011$
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Michel Devoret, Benjamin Huard, Robert Schoelkopf, and Leticia F. Cugliandolo

Print publication date: 2014

Print ISBN-13: 9780199681181

Published to Oxford Scholarship Online: September 2014

DOI: 10.1093/acprof:oso/9780199681181.001.0001

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Quantum noise and quantum measurement

Quantum noise and quantum measurement

(p.61) 2 Quantum noise and quantum measurement
Quantum Machines: Measurement and Control of Engineered Quantum Systems

A. Clerk

Oxford University Press

This chapter covers the basics of quantum noise and the subtle aspects of Caves’ theorem on quantum-limited amplifiers. It introduces on the one hand the susceptibilities of a quantum measurement system, and on the other the crucial Nyquist model of dissipation, which is essential to the understanding of the quantum fluctuation-dissipation theorem for a passive system and the constraints on noise for an active system. Great insight on the paradoxical properties of quantum noise can be obtained by comparing, in the calculation of the noise of an active circuit, the point of view of susceptibilities and response functions with the point of view of input-output theory dominated by the formalism of the scattering matrix. In particular, the chapter provides an explanation of the existence of different optimum working points for a nonmatched amplifier if one optimizes the gain or the noise.

Keywords:   quantum measurement, quantum noise, quantum-limited amplifier, dissipation, susceptibility, response function, input-output theory

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