Quantum Noise Limits for Nonlinear, Phase-Invariant Amplifiers

TL;DR

This paper investigates the noise limits of nonlinear, phase-invariant quantum amplifiers, showing they can outperform linear amplifiers in noise reduction and providing explicit examples and theoretical bounds.

Contribution

It introduces explicit examples of nonlinear, phase-invariant amplifiers and derives fundamental lower bounds on their noise generation.

Findings

Nonlinear amplifiers can generate less noise than linear ones.

Explicit examples of such amplifiers are provided.

Lower bounds on noise are derived for these amplifiers.

Abstract

Any quantum device that amplifies coherent states of a field while preserving their phase generates noise. A nonlinear, phase-invariant amplifier may generate less noise, over a range of input field strengths, than any linear amplifier with the same amplification. We present explicit examples of such nonlinear amplifiers, and derive lower bounds on the noise generated by a nonlinear, phase-invariant quantum amplifier.