Preparation of distilled and purified continuous variable entangled states

TL;DR

This paper demonstrates an experimental method for distilling and purifying continuous-variable entangled states of light, overcoming decoherence effects to improve quantum communication fidelity.

Contribution

It presents the first experimental realization of entanglement distillation in the continuous-variable regime with actual state preparation, enhancing quantum communication protocols.

Findings

Entanglement strength was successfully increased after distillation.

Purity of the states was improved through the process.

The method is suitable for enhancing quantum teleportation applications.

Abstract

The distribution of entangled states of light over long distances is a major challenge in the field of quantum information. Optical losses, phase diffusion and mixing with thermal states lead to decoherence and destroy the non-classical states after some finite transmission-line length. Quantum repeater protocols, which combine quantum memory, entanglement distillation and entanglement swapping, were proposed to overcome this problem. Here we report on the experimental demonstration of entanglement distillation in the continuous-variable regime. Entangled states were first disturbed by random phase fluctuations and then distilled and purified using interference on beam splitters and homodyne detection. Measurements of covariance matrices clearly indicate a regained strength of entanglement and purity of the distilled states. In contrast to previous demonstrations of entanglement distillation in the complementary discrete-variable regime, our scheme achieved the actual preparation of the distilled states, which might therefore be used to improve the quality of downstream applications such as quantum teleportation.