Thermal state quantum key distribution

TL;DR

This paper analyzes a thermal state quantum key distribution protocol using a beam splitter, demonstrating its potential for secure key generation even under attack, with detailed calculations and simulations confirming its robustness.

Contribution

It provides a detailed analysis of a thermal state CV-QKD protocol, including mutual information calculations and attack resilience, highlighting its experimental feasibility.

Findings

Positive lower bound on key rate under beam splitter attack

Thermal state protocol remains secure with nonzero beam proportion to Bob

Analytic and Monte Carlo methods agree on protocol performance

Abstract

We analyse a central broadcast continuous variable quantum key distribution protocol in which a beam produced by a thermal source is used to create a secret key between two parties, Alice and Bob. A beam splitter divides the initial beam into a pair of output beams, which are sent to Alice and Bob, with Eve intercepting Bob's beam. We investigate the protocol in detail, calculating mutual informations through a pair of analytic methods and comparing the results to the outputs of a Monte Carlo simulation of the protocol. In a lossless system, we find that a lower bound on the key rate remains positive in the protocol under a beam splitter attack, provided Bob receives a nonzero proportion of the beam initially sent to him. This suggests that the thermal state protocol could be used experimentally to produce secure keys.