Backflash light characterization to prevent QKD zero-error hacking

TL;DR

This paper investigates the backflash light emitted by single-photon avalanche diodes used in quantum key distribution, characterizes its properties, and proposes a solution to mitigate potential eavesdropping risks.

Contribution

The study provides a detailed spectral and temporal characterization of backflash light in InGaAs/InP SPADs and offers a method to reduce information leakage in QKD systems.

Findings

Backflash light can leak information in QKD systems.

Spectral and temporal properties of backflash vary with detector models.

Proposed mitigation reduces potential eavesdropping channels.

Abstract

Single photon avalanche diodes (SPADs) are the most commercially diffused solution for single-photon counting in quantum key distribution (QKD) applications. However, the secondary photon emission, arising from the avalanche of charge carriers during a photon detection, may be exploited by an eavesdropper to gain information without forcing errors in the transmission key. In this paper, we characterise such backflash light in gated InGaAs/InP SPADs, and its spectral and temporal characterization for different detector models and different operating parameters. We qualitatively bound the maximum information leakage due to backflash light, and propose a solution.