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arXiv · 1208.5174

Quantum limits on phase-preserving linear amplifiers

Carlton M. Caves·Joshua Combes·Zhang Jiang·Shashank Pandey
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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.

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Carlton M. Caves, Joshua Combes, Zhang Jiang, Shashank Pandey. 2012-08-25. Quantum limits on phase-preserving linear amplifiers. https://doi.org/10.1103/physreva.86.063802

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