Quantum-Limited Position Detection and Amplification: A Linear Response Perspective

TL;DR

This paper derives the fundamental quantum limits on the sensitivity of linear-response position detectors and amplifiers using a linear response framework, emphasizing noise, temperature, and damping effects.

Contribution

It introduces a linear response approach to determine the quantum limits of position detection and amplification, providing simple conditions for reaching these limits.

Findings

Derived quantum limit on detector sensitivity

Established conditions for quantum-limited amplification

Connected theoretical results to recent nanoelectromechanical experiments

Abstract

Using standard linear response relations, we derive the quantum limit on the sensitivity of a generic linear-response position detector, and the noise temperature of a generic linear amplifier. Particular emphasis is placed on the detector's effective temperature and damping effects; the former quantity directly determines the dimensionless power gain of the detector. Unlike the approach used in the seminal work of Caves [Phys. Rev. D, 26, 1817 (1982)], the linear-response approach directly involves the noise properties of the detector, and allows one to derive simple necessary and sufficient conditions for reaching the quantum limit. Our results have direct relevance to recent experiments on nanoelectromechanical systems, and complement recent theoretical studies of particular mesoscopic position detectors.