Quantum limits on noise for a class of nonlinear amplifiers

TL;DR

This paper introduces a class of quantum nonlinear amplifiers that achieve minimal noise addition, enabling near-ideal measurements of normal operators in the high-gain limit, bridging a gap in quantum amplification theory.

Contribution

The authors define a new class of quantum nonlinear amplifiers that add only half a quantum of noise and can perform ideal measurements of normal operators.

Findings

Amplifiers add only half a quantum of vacuum noise.

In high gain, they enable near-ideal measurements of normal operators.

They extend classical nonlinear amplification concepts into the quantum domain.

Abstract

Nonlinear amplifiers such as the transistor are ubiquitous in classical technology, but their quantum analogues are not well understood. We introduce a class of nonlinear amplifiers that amplify any normal operator and add only a half-quantum of vacuum noise at the output. In the large-gain limit, when used in conjunction with a noisy linear detector, these amplifiers implement ideal measurements of the normal operator.