A Passive and Self-Characterizing Cross-Encoded Receiver for Reference-Frame-Independent Quantum Key Distribution

TL;DR

This paper introduces a passive, self-characterizing receiver for reference-frame-independent quantum key distribution, enhancing security and simplifying implementation by employing time-bin to polarization conversion and quantum detector self-characterization.

Contribution

The work presents a novel passive receiver design for RFI-QKD that self-characterizes its measurement apparatus without tomography, improving security analysis and practical feasibility.

Findings

Successfully demonstrated a passive RFI-QKD receiver

Validated the measurement self-characterization technique

Confirmed the feasibility of the approach through a proof-of-principle experiment

Abstract

Quantum Key Distribution (QKD) promises to revolutionize the field of security in communication, with applications ranging from state secrets to personal data, making it a key player in the ongoing battle against cyber threats. Reference-Frame-Independent (RFI) QKD aims to simplify QKD implementations by allowing to reduce the requirements of alignment on a shared reference frame. This is done by performing two mutually unbiased measurements on the control states. In this work, we present a novel fully passive receiver for time-bin encoded RFI-QKD. Conversion of time-bin to polarization is employed to perform the required quantum measurement in a fully passive manner. Furthermore, to overcome experimental errors, we retrieved a complete description of our measurement apparatus by employing a recently introduced Quantum Detector Self-Characterization technique, without performing tomographic studies on the detection stage. In fact, the security analysis carried out in this work uses experimentally retrieved Positive Operator Valued Measurements, which consider our receiver defects, substituting the ideal expected operators and thus increasing the overall level of secrecy. Lastly, we conducted a proof-of-principle experiment that validated the feasibility of our method and its applicability to QKD applications.