Unconditional Security of Single-Photon Differential Phase Shift Quantum Key Distribution

In this Letter, we prove the unconditional security of the single-photon differential phase shift quantum key distribution (DPS-QKD) protocol, based on the conversion to an equivalent entanglement-based protocol. We estimate the upper bound of the phase error rate from the bit error rate, and show that the DPS-QKD protocol can generate an unconditionally secure key when the bit error rate is not greater than 4.12%. This proof is the first step to the unconditional security proof of a coherent state DPS-QKD.

Figure 1

Schematics of the 1-bit delay M-Z interferometer

Figure 2

Secure key generation rates per pulse (a) and per emitting photon (b) as a function of the total loss. Red solid line: $R_{\mathrm{BB}84}$; blue dashed line and green dash-dot line: $R_{\mathrm{DPS}}$ with $n=3$, 10, respectively; black dash-dot line and light blue solid line with triangles: $R_{\mathrm{IND}}$ with $n=3$, 10, respectively.