Interference at the Single Photon Level Along Satellite-Ground Channels

TL;DR

This paper demonstrates quantum interference of single photons over satellite-ground channels, confirming the feasibility of quantum experiments and communication in space at large distances and high relative speeds.

Contribution

It provides the first experimental observation of single photon interference involving moving satellites over thousands of kilometers.

Findings

Interference visibility up to 67% achieved

Successful real-time prediction of interference phase using laser ranging

Demonstrated quantum interference over 5000 km satellite-ground links

Abstract

Quantum interference arising from superposition of states is a striking evidence of the validity of Quantum Mechanics, confirmed in many experiments and also exploited in applications. However, as for any scientific theory, Quantum Mechanics is valid within the limits in which it has been experimentally verified. In order to extend such limits, it is necessary to observe quantum interference in unexplored conditions such as moving terminals at large distance in Space. Here we experimentally demonstrate single photon interference at a ground station due to the coherent superposition of two temporal modes reflected by a rapidly moving satellite thousand kilometers away. The relative speed of the satellite induces a varying modulation in the interference pattern. The measurement of the satellite distance in real time by laser ranging allowed us to precisely predict the instantaneous value of the interference phase. We then observed the interference patterns with visibility up to $67\%$ with three different satellites and with path length up to 5000 km. Our results attest the viability of photon temporal modes for fundamental tests of Physics and Quantum Communications in Space.