Mitigating imperfections in Differential Phase Shift Measurement-Device-Independent Quantum Key Distribution via Plug-and-Play architecture

Abstract: Measurement-device-independent quantum key distribution (MDI-QKD) was originally proposed as a means to address the issue of detector side-channel attacks and enable finite secure key rates over longer distances. However, the asymmetric characteristics of the channels from the two sources to the measurement device in MDI-QKD impose constraints on successfully extracting a secure key. In this work, we present a plug-and-play scheme for MDI-QKD based on differential phase shift (DPS) encoding. Specifically, we analyze the effects of pulse-width mismatch and polarization mismatch between the pulses arriving at the measurement device. The polarization mismatch is modeled with an assumption of sharing a common reference frame, and the maximum allowable mismatch is found to be 11 degrees. Furthermore, we show that a channel length asymmetry of 176.5 km results in Hong-Ou-Mandel interference visibility of 0.37, thereby leading to zero secure key rates for a polarization-based MDI-QKD protocol. We then present a plug-and-play architecture for DPS-MDI-QKD as a solution to some of these issues, thereby paving the way for practical implementations of MDI protocols.