Strong Einstein-Podolsky-Rosen entanglement from a single squeezed light source

TL;DR

This paper demonstrates the generation of strong EPR entanglement from a single squeezed light source at telecom wavelength, achieving high non-classical noise reduction and verifying EPR criteria with low optical loss.

Contribution

It provides the first experimental realization of high-quality EPR entanglement at 1550 nm using a single squeezed light source, with detailed analysis of loss requirements and potential for quantum communication.

Findings

Achieved up to 9.9 dB of squeezing at 1550 nm.

Observed EPR covariance product of 0.502, below the threshold of 1.

Identified loss threshold of 33.3% for observing EPR entanglement.

Abstract

Einstein-Podolsky-Rosen (EPR) entanglement is a criterion that is more demanding than just certifying entanglement. We theoretically and experimentally analyze the low resource generation of bi-partite continuous variable entanglement, as realized by mixing a squeezed mode with a vacuum mode at a balanced beam splitter, i.e. the generation of so-called vacuum-class entanglement. We find that in order to observe EPR entanglement the total optical loss must be smaller than 33.3 %. However, arbitrary strong EPR entanglement is generally possible with this scheme. We realize continuous wave squeezed light at 1550 nm with up to 9.9 dB of non-classical noise reduction, which is the highest value at a telecom wavelength so far. Using two phase controlled balanced homodyne detectors we observe an EPR co-variance product of 0.502 \pm 0.006 < 1, where 1 is the critical value. We discuss the feasibility of strong Gaussian entanglement and its application for quantum key distribution in a short-distance fiber network.