# Critical side channel effects in random bit generation with multiple semiconductor lasers in a polarization-based quantum key distribution system

## TL;DR

This paper investigates critical side channel vulnerabilities in polarization-based quantum key distribution systems using multiple semiconductor lasers, revealing how temporal and intensity disparities can compromise security and affect system performance.

## Contribution

It identifies previously unnoticed side channels in multi-laser QKD systems and provides experimental evidence of their impact on security and quantum bit error rate.

## Key findings

- Side channels due to temporal disparity and intensity fluctuation exist in multi-laser QKD.
- These side channels can significantly degrade security performance.
- Laser driving conditions influence the quantum bit error rate.

## Abstract

Most polarization-based BB84 quantum key distribution (QKD) systems utilize multiple lasers to generate one of four polarization quantum states randomly. However, random bit generation with multiple lasers can potentially open critical side channels, which significantly endangers the security of QKD systems. In this paper, we show unnoticed side channels of temporal disparity and intensity fluctuation, which possibly exist in the operation of multiple semiconductor laser diodes. Experimental results show that the side channels can enormously degrade security performance of QKD systems. An important system issue for the improvement of quantum bit error rate (QBER) related with laser driving condition is furtherly addressed with experimental results.