Nonlocal compensation of pure phase objects with entangled photons

TL;DR

This paper presents a method for nonlocal compensation of pure phase objects using entangled photons, enabling the restoration of entanglement and proposing a quantum key distribution protocol based on this technique.

Contribution

It introduces a scheme utilizing polarization and momentum entangled states for nonlocal phase compensation, demonstrated experimentally with a programmable spatial light modulator.

Findings

Purity and entanglement are reduced by phase objects but can be restored.

The setup enables a quantum key distribution protocol.

Experimental validation of nonlocal phase compensation.

Abstract

We suggest and demonstrate a scheme for coherent nonlocal compensation of pure phase objects based on two-photon polarization and momentum entangled states. The insertion of a single phase object on one of the beams reduces the purity of the state and the amount of shared entanglement, whereas the original entanglement can be retrieved by adding a suitable phase object on the other beam. In our setup polarization and momentum entangled states are generated by spontaneous parametric downconversion and then purified using a programmable spatial light modulator, which may be also used to impose arbitrary space dependent phase functions to the beams. As a possible application, we suggest and demonstrate a quantum key distribution protocol based on nonlocal phase compensation.