Efficient passive measurement-device-independent quantum key distribution

To date, only active-decoy-state methods have been adopted in current measurement-device-independent (MDI) quantum key distribution (QKD) protocols, causing security loopholes when modulating multiple light intensities with practical devices. To solve this problem, the passive-decoy-state method will be a good choice. Until today practical passive-decoy-state MDI QKD is still missing. In this paper, based on a recently discussed structure of heralded single-photon sources, we propose a passive-decoy-state MDI QKD protocol. In present work, one does not need to modulate light sources into different intensities, but utilizes the built-in local detection events to passively generate different decoy states. Furthermore, through carrying out an appropriate mathematical method, we are able to give very precise estimations for single-photon-pair contributions. As a result, our protocol can exhibit distinct advantages compared with state-of-the-art MDI QKD schemes even when the finite-key-size effect is taken into account. Therefore, our protocol seems a promising candidate to enhance both the security and performance of MDI QKD in practical implementation.

Figure 1

Schematic of our passive-decoy-state MDI QKD protocol: HSPS, heralded single-photon source; NC, nonlinear crystal; DM, dichroic mirror; BS, beam splitter; PBS, polarization beam splitter; PR, polarization rotator; $D_1$ and $D_2$, single-photon detectors.

Figure 2

Single-photon-pair yield $Y_{11}$ and phase-flip error rate $e_{11}^{ph}$ of different schemes. Here the data size $N_t={10}^9$.

Figure 3

Key rates of our scheme and two other reports of data size $N_t={10}^9$.

Figure 4

Key rates of different schemes versus data size at 50 km.