# Tools for the Performance Optimization of Single-Photon Quantum Key Distribution

## TL;DR

This paper demonstrates that temporal filtering of single-photon pulses can optimize quantum key distribution performance, improving secret key rates and security in practical quantum communication systems using realistic quantum light sources.

## Contribution

It introduces a method of temporal filtering for single-photon pulses that enhances QKD performance and provides real-time security monitoring using photon statistics analysis.

## Key findings

- Temporal filtering improves secret key fraction.
- Photon statistics analysis enables real-time security monitoring.
- The approach is applicable to various quantum communication implementations.

## Abstract

Quantum light sources emitting triggered single photons or entangled photon pairs have the potential to boost the performance of quantum key distribution (QKD) systems. Proof-of-principle experiments affirmed these prospects, but further efforts are necessary to push this field beyond its current status. In this work, we show that temporal filtering of single-photon pulses enables a performance optimization of QKD systems implemented with realistic quantum light sources, both in experiment and simulations. To this end, we analyze the influence of temporal filtering of sub-Poissonian single-photon pulses on the expected secret key fraction, the quantum bit error ratio, and the tolerable channel losses. For this purpose, we developed a basic QKD testbed comprising a triggered solid-state single-photon source and a receiver module designed for four-state polarization coding via the BB84 protocol. Furthermore, we demonstrate real-time security monitoring by analyzing the photon statistics, in terms of $g^{(2)}(0)$, inside the quantum channel by correlating the photon flux recorded at the four ports of our receiver. Our findings are useful for the certification of QKD and can be applied and further extended for the optimization of various implementations of quantum communication based on sub-Poissonian quantum light sources, including measurement-device-independent schemes of QKD as well as quantum repeaters. Our work represents an important contribution towards the development of QKD-secured communication networks based on quantum light sources.