Experimental study on discretely modulated continuous-variable quantum key distribution

TL;DR

This paper demonstrates a discretely modulated continuous-variable quantum key distribution system in free space, achieving high secret key rates by optimizing noise suppression and detection techniques.

Contribution

It introduces a practical free-space CV-QKD system with noise suppression and broadband detection, achieving high secret key rates under realistic conditions.

Findings

Secret key rate of 46.8 kbits/s at 90% loss

Amplitude noise suppressed to shot-noise limit

Phase noise has negligible impact on security

Abstract

We present a discretely modulated continuous-variable quantum key distribution system in free space by using strong coherent states. The amplitude noise in the laser source is suppressed to the shot-noise limit by using a mode cleaner combined with a frequency shift technique. Also, it is proven that the phase noise in the source has no impact on the final secret key rate. In order to increase the encoding rate, we use broadband homodyne detectors and the no-switching protocol. In a realistic model, we establish a secret key rate of 46.8 kbits/s against collective attacks at an encoding rate of 10 MHz for a 90% channel loss when the modulation variance is optimal.