Demonstration of reversible phase-insensitive optical amplifier

TL;DR

This paper demonstrates a reversible, phase-insensitive optical amplifier using linear optics and nonclassical ancillas, capable of approximate cloning and entanglement preservation, with potential applications in quantum information processing.

Contribution

It introduces a reversible linear optical amplifier with entanglement-based reversibility and approximate cloning, utilizing nonclassical ancillas and homodyne detection.

Findings

Achieved amplification gain of 2.0

Demonstrated approximate cloning with an anticlone present

Reconstructed initial states beyond the cloning limit

Abstract

We experimentally demonstrate phase-insensitive linear optical amplification which preserves the idler at the output. Since our amplification operation is unitary up to small excess noise, it is reversible beyond the classical limit. The entanglement between the two output modes is the resource for the reversibility. The amplification gain of 2.0 is demonstrated. In addition, combining this amplifier with a beamsplitter, we also demonstrate approximate cloning of coherent states where an anticlone is present. We investigate the reversibility by reconstructing the initial state from the output correlations, and the results are slightly beyond the cloning limit. Furthermore, full characterization of the amplifier and cloner is given by using coherent states with several different mean values as inputs. Our amplifier is based on linear optics, offline preparation of nonclassical ancillas, and homodyne measurements followed by feedforward. Squeezed states are used as the ancillas, and nonlinear optical effects are exploited only for their generation. The ancillas introduce nonclassicality into the amplifying operation, making entanglement at the output.