Implementation of a non-deterministic optical noiseless amplifier

TL;DR

This paper demonstrates a probabilistic, heralded optical amplifier that achieves noiseless amplification of coherent states, overcoming fundamental quantum noise limits through measurement-based techniques.

Contribution

It presents the first successful implementation of a non-deterministic, noiseless optical amplifier using quantum measurement and heralding, with full state characterization.

Findings

Achieved about 6dB gain in amplification.

Observed noise levels below the standard quantum limit.

Validated the approach with quantum homodyne tomography.

Abstract

Quantum mechanics imposes that any amplifier that works independently on the phase of the input signal has to introduce some excess noise. The impossibility of such a noiseless amplifier is rooted into unitarity and linearity of quantum evolution. A possible way to circumvent this limitation is to interrupt such evolution via a measurement, providing a random outcome able to herald a successful - and noiseless - amplification event. Here we show a successful realisation of such an approach; we perform a full characterization of an amplified coherent state using quantum homodyne tomography, and observe a strong heralded amplification, with about 6dB gain and a noise level significantly smaller than the minimal allowed for any ordinary phase-independent device.