Quantum noise limits for nonlinear, phase-invariant amplifiers
Quantum noise limits for nonlinear, phase-invariant amplifiers
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 …