Nonlocal restoration of two-mode squeezing in the presence of strong optical loss

TL;DR

This paper experimentally demonstrates that nonlocal correlations in entangled optical beams can be restored after severe loss by using an auxiliary entangled resource, confirming a theoretical prediction and advancing quantum communication techniques.

Contribution

The study provides the first experimental realization of nonlocal loss compensation in entangled beams using an auxiliary EPR state, validating a theoretical model.

Findings

Nonlocal correlations were restored after 50% loss.

Auxiliary EPR state effectively entangled the losses.

Quantum correlations were suppressed by loss but recovered with the resource.

Abstract

We present the experimental realization of a theoretical effect discovered by Olivares and Paris, in which a pair of entangled optical beams undergoing independent losses can see nonlocal correlations restored by the use of a nonlocal resource correlating the losses. Twin optical beams created in an entangled Einstein-Podolsky-Rosen (EPR) state by an optical parametric oscillator above threshold were subjected to 50% loss from beamsplitters in their paths. The resulting severe degradation of the signature quantum correlations observed between the two beams was then suppressed when another, independent EPR state impinged upon the other input ports of the beamsplitters, effectively entangling the losses inflicted to the initial EPR state. The additional EPR beam pair was classically coherent with the primary one but had no quantum correlations with it. This result may find applications as a quantum tap for entanglement.