Quantum limits on phase-preserving linear amplifiers
Abstract
The purpose of a phase-preserving linear amplifier is to make a small signal larger, regardless of its phase, so that it can be perceived by instruments incapable of resolving the original signal, while sacrificing as little as possible in signal-to-noise. Quantum mechanics limits how well this can be done: a high-gain linear amplifier must degrade the signal-to-noise; the noise added by the amplifier, when referred to the input, must be at least half a quantum at the operating frequency. This well-known quantum limit only constrains the second moments of the added noise. Here we derive the quantum constraints on the entire distribution of added noise: we show that any phase-preserving linear amplifier is equivalent to a parametric amplifier with a physical state for the ancillary mode; the noise added to the amplified field mode is distributed according to the Wigner function of the ancilla state.
Cite
@article{arxiv.1208.5174,
title = {Quantum limits on phase-preserving linear amplifiers},
author = {Carlton M. Caves and Joshua Combes and Zhang Jiang and Shashank Pandey},
journal= {arXiv preprint arXiv:1208.5174},
year = {2013}
}
Comments
37 pages, 6 figures