Twin Field QKD with 3-Pulse Differential Phase Encoding

Twin field quantum key distribution (TF-QKD) has attracted the attention of the research community thanks to its higher secure key rate which scales as square root of the channel transmittance. The twin field secure key rate thus crosses the repeaterless secure key rate distance bound, showing that the protocol can cater to large channel lengths. Here, we present a twin-field-like QKD protocol based on single photon interference of differential phase shift (DPS) encoded states and prove the security of the scheme. Our protocol builds upon an existing measurement device independent (MDI) QKD system that has a DPS encoding and modifies the sifting step to one based on single photon interference. We demonstrate security of our DPS-twin-field (DPS-TF) protocol against collective attacks and quantify the secure key rate. We find that with the current state-of-the-art technology, both TF-QKD and MDI-QKD protocols with the DPS encoding work almost identically in terms of the channel length, although the achievable secure key rate of the DPS-TF QKD is higher compared to MDI-QKD.