Atmospheric continuous-variable quantum communication

TL;DR

This study demonstrates the feasibility of continuous-variable quantum communication over a 1.6 km urban free-space link, showing atmospheric effects can be effectively managed for secure quantum key distribution.

Contribution

We experimentally show atmospheric CV quantum communication with auto-compensation of fluctuations, optimizing state parameters for high entanglement transmission in urban conditions.

Findings

Effective auto-compensation removes atmospheric disturbances

Optimal state amplitudes enhance entanglement distribution

High entanglement rates indicate potential for CV QKD

Abstract

We present a quantum communication experiment conducted over a point-to-point free-space link of 1.6 km in urban conditions. We study atmospheric influences on the capability of the link to act as a continuous-variable (CV) quantum channel. Continuous polarization states (that contain the signal encoding as well as a local oscillator in the same spatial mode) are prepared and sent over the link in a polarization multiplexed setting. Both signal and local oscillator undergo the same atmospheric fluctuations. These are intrinsically auto-compensated which removes detrimental influences on the interferometric visibility. At the receiver, we measure the Q-function and interpret the data using the framework of effective entanglement. We compare different state amplitudes and alphabets (two-state and four-state) and determine their optimal working points with respect to the distributed effective entanglement. Based on the high entanglement transmission rates achieved, our system indicates the high potential of atmospheric links in the field of CV QKD.