An ultra-sensitive balanced detector with low noise for continuous-variable quantum key distribution

TL;DR

This paper introduces a highly sensitive, low-noise balanced detector with enhanced gain, bandwidth, and common mode rejection, suitable for continuous-variable quantum key distribution, outperforming commercial detectors in noise and shot-noise ratio.

Contribution

The paper presents a novel balanced detector design with two-stage amplification and JFET integration, achieving lower noise and higher CMRR than existing commercial detectors.

Findings

Noise voltage RMS of about 6 mV at high gain

Shot-noise to electronic-noise ratio of 16.8 dB

CMRR of 53 dB, surpassing commercial detectors

Abstract

A well-balanced detector with high sensitivity and low noise is presented in this paper. The two-stage amplification structure is used to increase electronic gain while keeping an effective bandwidth of about 70 MHz. In order to further reduce electronic noise, a junction field-effect transistor(JFET) is connected between photodiodes and transimpedance amplifier to reduce the impact of amplifier leakage current. Benefit from these designs, the root-mean-square(RMS) of noise voltage is about 6 mV with a gain of 3.2E5 V/W, and it means an ultra-low noise equivalent power density of 2.2E-12 W/rtHz, only half of common low-noise commercial detectors. In addition, two photodiodes in similar frequency response are selected for detector and make the common mode rejection ratio(CMRR) of detector reached 53 dB, about 13 dB higher than commercial detectors. Further tests indicate that 16.8 dB shot-noise to electronic-noise ratio is measured in our detector, which is better than most high speed balanced detectors.