Numerical Assessment and Optimization of Discrete-Variable Time-Frequency Quantum Key Distribution

TL;DR

This paper numerically evaluates a discrete-variable time-frequency quantum key distribution protocol, analyzing how the number of symbols and pulse relations affect key rate and security against eavesdropping.

Contribution

It provides the first numerical assessment of DV-TF-QKD, identifying optimal parameters for maximizing key rate and security without a complete security proof.

Findings

Secret key rate increases with more symbols per basis

Optimal pulse relations improve key rate and security

Higher symbols per basis enhance protocol performance

Abstract

The discrete variables (DV) time-frequency (TF) quantum key distribution (QKD) protocol is a BB84 like protocol, which utilizes time and frequency as complementary bases. As orthogonal modulations, pulse position modulation (PPM) and frequency shift keying (FSK) are capable of transmitting several bits per symbol, i.e. per photon. However, unlike traditional binary polarization shift keying, PPM and FSK do not allow perfectly complementary bases. So information is not completely deleted when the wrong-basis filters are applied. Since a general security proof does not yet exist, we numerically assess DV-TF-QKD. We show that the secret key rate increases with a higher number of symbols per basis. Further we identify the optimal pulse relations in the two bases in terms of key rate and resistance against eavesdropping attacks.