Experimental Asynchronous Measurement-Device-Independent Quantum Cryptographic Conferencing

TL;DR

This paper demonstrates an experimental three-user asynchronous measurement-device-independent quantum cryptographic conferencing protocol that significantly improves key rate scalability, paving the way for large-scale quantum networks.

Contribution

It introduces and experimentally implements an asynchronous MDI QCC protocol with enhanced key rate scalability independent of user number.

Findings

Achieved a key rate of approximately 4.470×10^{-9} bits per pulse.

Implemented the protocol without global phase tracking using FFT-based frequency difference estimation.

Demonstrated the protocol's robustness under a maximum loss of 59.6 dB.

Abstract

The quantum cryptographic conferencing (QCC) protocol, which distributes identical secure keys to user groups, is a crucial component of the quantum network. Previous experimental works have implemented the measurement-device-independent (MDI) QCC, of which the key rate in an $N$-user network scales down as $R\sim O(\eta^N)$, respectively. Building on the MDI QCC protocol, the asynchronous MDI (AMDI) QCC protocol theoretically integrates the mode pairing scheme into QCC, significantly boosting the key rate to $R\sim O(\eta)$, which is independent of the number of users, and thus demonstrating greater application potential. Experimentally, in this work, we implement the three-user AMDI QCC network without global phase tracking by adopting the fast Fourier transform-based frequency difference estimation and the phase drift compensation technique. Finally, we achieve a key rate of about $4.470\times10^{-9}$ bits per pulse under a maximum overall loss of about 59.6 dB. This work provides a scalable solution for the development of large-scale quantum communication networks in the future.