Composably secure time-frequency quantum key distribution

TL;DR

This paper provides a rigorous, composable security proof for a high-dimensional time-frequency quantum key distribution protocol using spectrally entangled photons, enabling secure high-rate communication over metropolitan distances.

Contribution

It introduces the first composable security proof for TFQKD that accounts for finite-size effects and arbitrary attacks, extending beyond previous Gaussian attack assumptions.

Findings

Key rates of several Mbits/s over 40 km

Maximum secure transmission distance up to 140 km

Security proof applicable to arbitrary attacks

Abstract

We present a composable security proof, valid against arbitrary attacks and including finite-size effects, for a high dimensional time-frequency quantum key distribution (TFQKD) protocol based upon spectrally entangled photons. Previous works have focused on TFQKD schemes as it combines the impressive loss tolerance of single-photon QKD with the large alphabets of continuous variable (CV) schemes, which enables the potential for more than one bit of secret key per transmission. However, the finite-size security of such schemes has only been proven under the assumption of collective Gaussian attacks. Here, by combining recent advances in entropic uncertainty relations for CVQKD with decoy state analysis, we derive a composable security proof that predicts key rates on the order of Mbits/s over metropolitan distances (40km or less) and maximum transmission distances of up to 140km.