Detecting correlated errors in twin-field quantum key distribution

TL;DR

This paper demonstrates an experimental method to detect correlated errors in a twin-field quantum key distribution system using a technique related to self-consistent tomography, enhancing security analysis without trusting third-party measurements.

Contribution

The authors introduce a practical approach to identify correlated errors in TFQKD systems without requiring trust in the measurement device, improving security verification methods.

Findings

Successfully detected correlated errors in a fiber-Sagnac loop TFQKD system.

Enabled error detection while trusting only local states, not third-party measurements.

Validated the technique's effectiveness through experimental implementation.

Abstract

We experimentally demonstrate that we can detect correlated errors in a twin-field quantum key distribution (TFQKD) system by using a technique that is related to self-consistent tomography. We implement a TFQKD system based on a fiber-Sagnac loop, in which Alice and Bob encode information in the phase of weak coherent states that propagate in opposite directions around the loop. These states interfere as they exit the loop and are detected by a third party, Charlie, who reports the results of their measurements to Alice and Bob. We find that it is possible for Alice and Bob to detect correlated state-preparation and measurement errors while trusting only their own individual states, and without trusting Charlie's measurements.