Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Quantum noise and quantum measurement

Aashish A. Clerk

Published Jun 12, 2014• 5 citations
Publisher

Abstract

Abstract 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.

DOI
10.1093/acprof:oso/9780199681181.003.0002

Related papers

Quantum limit in continuous quantum measurement

Cheng-gang Shao

An inequality about quantum noise is presented with the imprecise measurement theory, which is used to analyse the quantum limit in continuous quantum measurement. Different from the linear-response approach based on the quantum relation between noise and susceptibilities of the detector, we provide an explicit functional relation between quantum noise and reduction operator, and show a rigorous result: The minimum noise added by the detector in quantum measurement is precisely equal to the zero-point noise. This conclusion generalizes the standard Haus-Caves quantum limit for a linear amplifier. We also discuss the statistic characters of the back-action force in quantum measurement and show on how to reach the quantum limit.

arXiv:1202.4065•Feb 18, 2012•0 citations

Quantum noise in ideal operational amplifiers

Jean-Michel Courty, Francesca Grassia, Serge Reynaud

We consider a model of quantum measurement built on an ideal operational amplifier operating in the limit of infinite gain, infinite input impedance and null output impedance and with a feedback loop. We evaluate the intensity and voltage noises which have to be added to the classical amplification equations in order to fulfill the requirements of quantum mechanics. We give a description of this measurement device as a quantum network scattering quantum fluctuations from input to output ports.

arXiv:quant-ph/9811062•Europhysics Letters (EPL)•Apr 1, 1999•14 citations

Quantum noise in ideal operational amplifiers

Jean-Michel Courty, Francesca Grassia, Serge Reynaud

We consider a model of quantum measurement built on an ideal operational amplifier operating in the limit of infinite gain, infinite input impedance and null output impedance and with a feddback loop. We evaluate the intensity and voltage noises which have to be added to the classical amplification equations in order to fulfill the requirements of quantum mechanics. We give a description of this measurement device as a quantum network scattering quantum fluctuations from input to output ports.

•Jan 1, 1999•13 citations

Fluctuations and correlations

Tero Tapio Heikkilä

This chapter deals with noise: time-dependent fluctuation of observables at or out of equilibrium. The main emphasis is on current noise. The chapter explains the use of the correlation function, the fluctuation-dissipation theorem, and thermal and vacuum fluctuations. It describes shot noise produced in out-of-equilibrium setups with a simple Schottky model, with the microscopic scattering and Boltzmann-Langevin approaches. The chapter also discusses the Langevin approach of describing coupling of noise in electrical circuits and a related description of noise measurements, and briefly explains the theory for cross correlations. The second part of the chapter discusses effects of noise on quantum systems – energy relaxation and dephasing. The chapter concludes by presenting the theory of full counting statistics and briefly describes heat current noise.

Oxford University Press eBooks•Jan 31, 2013•2 citations

Quantum limits on noise in linear amplifiers

Carlton M. Caves

How much noise does quantum mechanics require a linear amplifier to add to a signal it processes? An analysis of narrow-band amplifiers (single-mode input and output) yields a fundamental theorem for phase-insensitive linear amplifiers; it requires such an amplifier, in the limit of high gain, to add noise which, referred to the input, is at least as large as the half-quantum of zero-point fluctuations. For phase-sensitive linear amplifiers, which can respond differently to the two quadrature phases ("$cos\ensuremath{\omega}t$" and "$sin\ensuremath{\omega}t$"), the single-mode analysis yields an amplifier uncertainty principle---a lower limit on the product of the noises added to the two phases. A multimode treatment of linear amplifiers generalizes the single-mode analysis to amplifiers with nonzero bandwidth. The results for phase-insensitive amplifiers remain the same, but for phase-sensitive amplifiers there emerge bandwidth-dependent corrections to the single-mode results. Specifically, there is a bandwidth-dependent lower limit on the noise carried by one quadrature phase of a signal and a corresponding lower limit on the noise a high-gain linear amplifier must add to one quadrature phase. Particular attention is focused on developing a multimode description of signals with unequal noise in the two quadrature phases.

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields•Oct 15, 1982•1,723 citations

Quantum Measurement

Andrew N. Jordan, Irfan A. Siddiqi

This book adopts a novel, physics-first approach to quantum measurement, using physical experiments as the basis to describe the underlying mathematical formalism. Topics covered include weak measurements, quantum measurement reversal, quantum trajectories and the stochastic path integral formalism. The theory of quantum measurement is also covered in detail, including discussion of how it can be tested and demonstrated in a laboratory: how to build quantum-limited amplifiers, fundamental noise limits imposed on measurement by quantum mechanics, and the design of superconducting circuits. This text is an excellent introduction for students with a basic understanding of quantum mechanics wanting to learn more about measurement theory, and the inclusion of a wide selection of end-of-chapter exercises make this book ideal for emerging courses on the topic. Key chapters introducing the foundations of quantum computing and the history of measurement theory are equally accessible to a broader, less specialised audience.

Cambridge University Press eBooks•Feb 15, 2024•55 citations
Abstract 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.
An inequality about quantum noise is presented with the imprecise measurement theory, which is used to analyse the quantum limit in continuous quantum measurement. Different from the linear-response approach based on the quantum relation between noise and susceptibilities of the detector, we provide an explicit functional relation between quantum noise and reduction operator, and show a rigorous result: The minimum noise added by the detector in quantum measurement is precisely equal to the zero-point noise. This conclusion generalizes the standard Haus-Caves quantum limit for a linear amplifier. We also discuss the statistic characters of the back-action force in quantum measurement and show on how to reach the quantum limit.
This chapter deals with noise: time-dependent fluctuation of observables at or out of equilibrium. The main emphasis is on current noise. The chapter explains the use of the correlation function, the fluctuation-dissipation theorem, and thermal and vacuum fluctuations. It describes shot noise produced in out-of-equilibrium setups with a simple Schottky model, with the microscopic scattering and Boltzmann-Langevin approaches. The chapter also discusses the Langevin approach of describing coupling of noise in electrical circuits and a related description of noise measurements, and briefly explains the theory for cross correlations. The second part of the chapter discusses effects of noise on quantum systems – energy relaxation and dephasing. The chapter concludes by presenting the theory of full counting statistics and briefly describes heat current noise.
How much noise does quantum mechanics require a linear amplifier to add to a signal it processes? An analysis of narrow-band amplifiers (single-mode input and output) yields a fundamental theorem for phase-insensitive linear amplifiers; it requires such an amplifier, in the limit of high gain, to add noise which, referred to the input, is at least as large as the half-quantum of zero-point fluctuations. For phase-sensitive linear amplifiers, which can respond differently to the two quadrature phases ("$cos\ensuremath{\omega}t$" and "$sin\ensuremath{\omega}t$"), the single-mode analysis yields an amplifier uncertainty principle---a lower limit on the product of the noises added to the two phases. A multimode treatment of linear amplifiers generalizes the single-mode analysis to amplifiers with nonzero bandwidth. The results for phase-insensitive amplifiers remain the same, but for phase-sensitive amplifiers there emerge bandwidth-dependent corrections to the single-mode results. Specifically, there is a bandwidth-dependent lower limit on the noise carried by one quadrature phase of a signal and a corresponding lower limit on the noise a high-gain linear amplifier must add to one quadrature phase. Particular attention is focused on developing a multimode description of signals with unequal noise in the two quadrature phases.
This book adopts a novel, physics-first approach to quantum measurement, using physical experiments as the basis to describe the underlying mathematical formalism. Topics covered include weak measurements, quantum measurement reversal, quantum trajectories and the stochastic path integral formalism. The theory of quantum measurement is also covered in detail, including discussion of how it can be tested and demonstrated in a laboratory: how to build quantum-limited amplifiers, fundamental noise limits imposed on measurement by quantum mechanics, and the design of superconducting circuits. This text is an excellent introduction for students with a basic understanding of quantum mechanics wanting to learn more about measurement theory, and the inclusion of a wide selection of end-of-chapter exercises make this book ideal for emerging courses on the topic. Key chapters introducing the foundations of quantum computing and the history of measurement theory are equally accessible to a broader, less specialised audience.