Photonic interface between subcarrier wave and dual rail encodings

Quantum key distribution with multimode subcarrier wave encoding is propitious for being robust against environmental disturbance. For application in long-distance quantum communications this encoding has to be compatible with entanglement-assisted quantum repeaters that are commonly designed to work with dual rail encodings. We propose and demonstrate an interface between subcarrier wave and dual rail encodings with a fidelity of more than 92% using a linear optical circuit. The developed scheme may find an application in future heterogeneous quantum networks that combine quantum key distribution with trusted and non-trusted nodes.