Encoding converters for quantum communication networks

Quantum communication networks, such as quantum key distribution (QKD) networks, typically employ the measurement-resend mechanism between two users using quantum communication devices based on different quantum encoding types. To achieve direct communication between the devices with different quantum encoding types, in this paper, we propose encoding conversion schemes between the polarization bases (rectilinear, diagonal and circular bases) and the time-bin phase bases (two phase bases and time-bin basis) and design the quantum encoding converters. The theoretical analysis of the encoding conversion schemes is given in detail, and the basis correspondence of encoding conversion and the property of bit flip are revealed. The conversion relationship between polarization bases and time-bin phase bases can be easily selected by controlling a phase shifter. Since no optical switches are used in our scheme, the converter can be operated with high speed. The converters can also be modularized, which may be utilized to realize miniaturization in the future.