Quantum Noise Limits for Nonlinear, Phase-Invariant 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.

RevTeX, 6 pages + 4 figures (included in file; hard copy sent on request)

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