Detector Asymmetry in Continuous Variable Quantum Key Distribution

TL;DR

This paper investigates how asymmetry in heterodyne detectors impacts phase estimation accuracy in CV-QKD systems, quantifies its effects, and proposes methods to mitigate this issue to improve transmission distance and key rate.

Contribution

It introduces a method to counteract detector asymmetry effects in CV-QKD, enhancing system performance and reliability.

Findings

Detection asymmetry reduces phase estimation accuracy.

Counteracting methods improve transmission distance.

Quantum optical tomography validates the effects.

Abstract

In Local-local Oscillator (LLO) based Continuous-Variable Quantum Key Distribution (CV-QKD), the phase reference of the transmitter and receiver, Alice and Bob, are naturally de-correlated due to their use of individual lasers. A phase reference signal is used, whose measurement is critical for estimating the phase difference and correcting the raw QKD data. We observed that asymmetry in the quadrature measurements of the shot noise-limited heterodyne detector affects the accuracy of the reference signal's phase estimation and thereby reduces the achievable transmission distance and key rate of the CV-QKD system. We quantify the effect and propose a method to counteract the effect of detection asymmetry. We also evaluate the effects of detection asymmetry using quantum optical tomography.