High-speed Gaussian modulated continuous-variable quantum key distribution with a local local oscillator based on pilot-tone-assisted phase compensation

TL;DR

This paper demonstrates a high-speed Gaussian modulated CVQKD system with a local local oscillator, utilizing pilot-tone-assisted phase compensation and heterodyne detection to achieve secure key rates over 25 km fiber.

Contribution

It introduces a novel LLO-CVQKD scheme with multiplexing and real-time phase noise compensation, enabling simultaneous quadrature measurement without basis switching.

Findings

Achieved a secure key rate of 7.04 Mbps over 25 km fiber.

Real-time phase noise compensation reduces excess noise.

Demonstrated high-speed quantum key distribution with heterodyne detection.

Abstract

A high-speed Gaussian modulated continuous-variable quantum key distribution (CVQKD) with a local local oscillator (LLO) is experimentally demonstrated based on pilot-tone-assisted phase compensation. In the proposed scheme, the frequency-multiplexing and polarization-multiplexing techniques are used for the separate transmission and heterodyne detection between quantum signal and pilot tone, guaranteeing no crosstalk from strong pilot tone to weak quantum signal and different detection requirements of low-noise for quantum signal and high-saturation limitation for pilot tone. Moreover, compared with the conventional CVQKD based on homodyne detection, the proposed LLO-CVQKD scheme can measure X and P quadrature simultaneously using heterodyne detection without need of extra random basis selection. Besides, the phase noise, which contains the fast-drift phase noise due to the relative phase of two independent lasers and the slow-drift phase noise introduced by quantum channel disturbance, has been compensated experimentally in real time, so that a low level of excess noise with a 25km optical fiber channel is obtained for the achievable secure key rate of 7.04 Mbps in the asymptotic regime and 1.85 Mbps under the finite-size block of 10^7.