Tools for the performance optimization of single-photon quantum key distribution

Timm Kupko,Jan-Hindrik Schulze,Stephan Reitzenstein,Tobias Heindel,Sven Rodt,Lucas Rickert,Martin Von Helversen,Manuel Gschrey,André Strittmatter

doi:10.1038/s41534-020-0262-8

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.

Highlights

Privacy in communication is an increasingly important challenge in our information-driven society[1]
The respective quantum light sources ideally required for Quantum key distribution (QKD), had been impossible to fabricate with sufficient brightness and quality for a long time
We consider the results presented in this work an important contribution towards the development of QKD-secured communication networks based on quantum light sources

Summary

INTRODUCTION

Privacy in communication is an increasingly important challenge in our information-driven society[1]. Based SPS and a receiver module designed for four-state polarization coding via the BB84 protocol Using this Bob module in combination with our SPS, we determine the sifted key fraction, the quantum bit error ratio (QBER) caused by the receiver, and the g(2)(0) of the single-photon pulses inside the quantum channel, to extract the secure key rate expected in full implementations of QKD. We show that optimal performance for a given SPS can be achieved by carefully setting Bob’s acceptance time windows, depending on the pulse shape and noise level This can be either used to maximize the secure key rate for a given channel loss or to extend the maximally tolerable loss, i.e. the achievable communication distance. We record the photon arrival time distribution at the four

RESULTS

DISCUSSION

Findings

METHODS