Quantum-correlation-based free-space optical link with an active reflector

TL;DR

This paper demonstrates a quantum optical communication link over 250 meters outdoors, using an active reflector and laser tracking to mitigate atmospheric turbulence effects for reliable quantum information transfer.

Contribution

It introduces a novel outdoor quantum FSO link with active beam steering and feedback control to counteract atmospheric disturbances.

Findings

Successful quantum link over 250 meters outdoors

Effective beam correction using laser tracking and active reflector

Potential for real-world urban quantum communication

Abstract

We present a quantum-correlation-based free-space optical(FSO) link over 250 m using an outdoor active reflector 125 m from the transceiver station. The performance of free-space optical communication can be significantly degraded by atmospheric turbulence effects, such as beam wander and signal fluctuations. We used a 660 nm tracking laser to reduce atmospheric effects, by analyzing the fast beam wander and slow temporal beam drift, using this information to correct the quantum channel alignment of the 810 nm signal photons. In this work, the active reflector consisted of a mirror, a 6-axis hexapod stage, and a long-range wireless bridge. The slow drift of the beam path due to outdoor temperature changes was steered and controlled using wireless optical feedback between the receiver units and the active reflector. Our work provides useful knowledge for improved control of beam paths in outdoor conditions, which can be developed to ensure high quality quantum information transfer in real-world scenarios, such as an unmanned FSO link for urban quantum communication or retro-reflective quantum communication links.