Improving the Secure Key Rate and Error Tolerance of the Interferometer-Based Time-Frequency Encoding QKD System

Abstract

The interferometer-based, time-frequency encoding quantum key distribution (TF-QKD) scheme is a promising way to loosen up the restrict resolution requirement for the temporal measurement in TF-QKD protocol. However, the utilization of delay interferometers in the existing schemes causes lower efficiency of the frequency measurement, so it would decrease the secure key generation rate and the error tolerance. In order to improve this imperfection, we propose two kinds of schemes, one is the pre-balance TF scheme (PB-TF), in which Alice actively adjusts the probability distributions of sending photons encoded in two bases. The other one is the non-delay interferometer based TF scheme (NDI-TF), in this scheme the signals are converted from serial to parallel before entering the interferometers which eliminates the extra loss of the frequency measurement with delay interferometers. We theoretically verify the performance improvement of both schemes and discuss their advantages under the practical application scenario. The simulation results show that both of the schemes can improve the secure key generation rate and the error tolerance, but the NDI-TF scheme has higher secure key generation rate especially in the high-dimensional encoding QKD systems. As for the low-dimensional system, the PB-TF scheme is preferred since its performance is comparable to the NDI-TF scheme but with low cost and easy to implement.