A balanced homodyne detector for high-rate Gaussian-modulated coherent-state quantum key distribution

TL;DR

This paper analyzes and improves the security of Gaussian-modulated coherent-state QKD by considering excess noise factors, and demonstrates a high-speed balanced homodyne detector capable of high secure key rates.

Contribution

It introduces a refined realistic model for GMCS QKD accounting for excess noise and presents a high-speed balanced homodyne detector with experimental validation.

Findings

The homodyne detector has a 104MHz bandwidth.

Electronic noise is 13dB below shot noise.

Secure key rate can reach Mbps over a few kilometers.

Abstract

We discuss excess noise contributions of a practical balanced homodyne detector in Gaussian-modulated coherent-state (GMCS) quantum key distribution (QKD). We point out the key generated from the original realistic model of GMCS QKD may not be secure. In our refined realistic model, we take into account excess noise due to the finite bandwidth of the homodyne detector and the fluctuation of the local oscillator. A high speed balanced homodyne detector suitable for GMCS QKD in the telecommunication wavelength region is built and experimentally tested. The 3dB bandwidth of the balanced homodyne detector is found to be 104MHz and its electronic noise level is 13dB below the shot noise at a local oscillator level of 8.5*10^8 photon per pulse. The secure key rate of a GMCS QKD experiment with this homodyne detector is expected to reach Mbits/s over a few kilometers.