Experimental Single-Photon Transmission from Satellite to Earth

TL;DR

This paper demonstrates the successful transmission of near-single photons from a satellite to Earth over 400 km, achieving high signal-to-noise ratio suitable for secure quantum communication.

Contribution

It provides the first direct experimental evidence of satellite-ground single-photon transmission with high SNR under realistic conditions.

Findings

Achieved SNR > 16:1 for satellite-to-ground photon transmission

Demonstrated 0.85 photons per pulse over 400 km link

Enabled secure quantum key distribution potential

Abstract

Free-space quantum communication with satellites opens a promising avenue for global secure quantum network and large-scale test of quantum foundations. Recently, numerous experimental efforts have been carried out towards this ambitious goal. However, one essential step - transmitting single photons from the satellite to the ground with high signal-to-noise ratio (SNR) at realistic environments - remains experimental challenging. Here, we report a direct experimental demonstration of the satellite-ground transmission of a quasi-single-photon source. In the experiment, single photons (~0.85 photon per pulse) are generated by reflecting weak laser pulses back to earth with a cube-corner retro-reflector on the satellite Champ, collected by a 600-mm diameter telescope at the ground station, and finally detected by single-photon counting modules (SPCMs) after 400-km free-space link transmission. With the help of high accuracy time synchronization, narrow receiver field-of-view (FOV) and high-repetition-rate pulses (76 MHz), a SNR of better than 16:1 is obtained, which is sufficient for a secure quantum key distribution. Our experimental results represent an important step towards satellite-ground quantum communication.