A Bipartite Quantum Key Distribution Protocol Based on Indefinite Causal Order

TL;DR

This paper introduces a novel bipartite quantum key distribution protocol leveraging indefinite causal order, achieving high raw key matching probability and analyzing practical implementations with various scenarios.

Contribution

It presents the first QKD protocol based on causal nonseparability and indefinite causal order, expanding quantum communication methods.

Findings

Achieves 85.35% raw key matching probability.

Compatible with standard error correction.

Analyzes multiple practical scenarios for implementation.

Abstract

We propose a bipartite quantum key distribution (QKD) protocol based on causal nonseparability: the presence of a resource -- a process matrix -- that does not correspond to any definite causal order between two parties. In our protocol, Alice and Bob perform local operations arranged in a ``causal-order guessing game,'' whereby each round yields an 85.35\% probability of matching bits when the communication is undisturbed. This raw matching probability (or equivalently, a $\sim14.65\%$ error rate) is amenable to standard forward error-correction strategies. We further discuss the practical construction of the QKD protocol using indefinite causal order, where several different scenarios are deeply analyzed.