Protocol choice and parameter optimization in decoy-state measurement-device-independent quantum key distribution

TL;DR

This paper compares decoy-state methods in MDI-QKD, showing two decoy states are nearly optimal, and demonstrates that full system parameter optimization significantly enhances key rate, with a fast local search method proposed.

Contribution

It provides a comprehensive comparison of decoy-state protocols and introduces an efficient local search method for parameter optimization in MDI-QKD.

Findings

Two decoy states suffice for near-optimal key rate.

Full parameter optimization can increase key rate by over ten times.

A fast local search method outperforms exhaustive search in speed.

Abstract

Measurement-device-independent quantum key distribution (MDI-QKD) has been demonstrated in both laboratories and field-tests using attenuated lasers combined with the decoy-state technique. Although researchers have studied various decoy-state MDI-QKD protocols with two or three decoy states, a clear comparison between these protocols is still missing. This invokes the question of how many types of decoy states are needed for practical MDI-QKD. Moreover, the system parameters to implement decoy-state MDI-QKD are only partially optimized in all previous works, which casts doubt on the actual performance of former demonstrations. Here, we present analytical and numerical decoy-state methods with one, two and three decoy states. We provide a clear comparison among these methods and find that two decoy states already enable a near optimal estimation and more decoy states cannot improve the key rate much in either asymptotic or finite-data settings. Furthermore, we perform a full optimization of system parameters and show that full optimization can significantly improve the key rate in the finite-data setting. By simulating a real experiment, we find that full optimization can increase the key rate by more than one order of magnitude compared to non-optimization. A local search method to optimize efficiently the system parameters is proposed. This method can be four orders of magnitude faster than a trivial exhaustive search to achieve a similar optimal key rate. We expect that this local search method could be valuable for general fields in physics.