High-fidelity transmission of entanglement over a high-loss freespace channel

TL;DR

This paper reports the experimental demonstration of transmitting entangled photon pairs over a 144 km free-space link with high fidelity despite extreme atmospheric attenuation, supporting future satellite-based quantum communication.

Contribution

It is the first to experimentally show high-fidelity entanglement transmission over a high-loss, turbulent free-space channel comparable to satellite communication scenarios.

Findings

Received entangled states maintain high fidelity despite 64 dB loss.

The entangled photons violate the CHSH inequality by over 5 standard deviations.

Photons are not significantly decohered during 0.5 ms flight through air.

Abstract

Quantum entanglement enables tasks not possible in classical physics. Many quantum communication protocols require the distribution of entangled states between distant parties. Here we experimentally demonstrate the successful transmission of an entangled photon pair over a 144 km free-space link. The received entangled states have excellent, noise-limited fidelity, even though they are exposed to extreme attenuation dominated by turbulent atmospheric effects. The total channel loss of 64 dB corresponds to the estimated attenuation regime for a two-photon satellite quantum communication scenario. We confirm that the received two-photon states are still highly entangled by violating the CHSH inequality by more than 5 standard deviations. From a fundamental point of view, our results show that the photons are virtually not subject to decoherence during their 0.5 ms long flight through air, which is encouraging for future world-wide quantum communication scenarios.