为了进一步提高测量设备无关量子密钥分发(MDI-QKD)系统的传输距离和密钥率, 将脉冲位置调制(PPM)技术引入到MDI-QKD中, 利用弱光源中的空脉冲和高维编码技术, 提出了一种高效的测量设备无关量子密钥分发, 即PPM-MDI-QKD协议.协议中, 通信双方首先将M个连续的弱脉冲构建成一个PPM帧, 然后利用BB84极化编码和PPM编码方案实现高维编码, 最后根据合法PPM帧、成功贝尔态测量结果以及匹配基筛选出安全密钥.数值计算结果表明, 当光源平均光强小于0.13时, PPM-MDI-QKD协议的性能优于MDI-QKD协议; 与迄今为止报道的最远404 km的MDI-QKD协议相比, 在相同条件下, 本协议最远传输距离能够达到480 km, 在404 km传输距离上的密钥率可达5.4×10－4 bps.

In order to further enhance the transmission distance and secret key rate of the Measurement-Device-Independent Quantum Key Distribution (MDI-QKD) system, the Pulse Position Modulation (PPM) technique is introduced to the MDI-QKD protocol, and a new efficient quantum key distribution protocol, named PPM-MDI-QKD protocol, is proposed by utilizing the empty pulses of the weak source and high dimensional encoding technology. In the protocol, two communication parties firstly construct a PPM frame consisting of M consecutive weak pulses, then combine the BB84 polarization encoding and PPM encoding schemes to operate high dimensional encoding, and finally sift out the secure key with the legal PPM frame, the successful Bell-state measurement results, and matched bases. The numerical results show that the PPM-MDI-QKD protocol outperforms MDI-QKD protocol when the intensity of signals is less than 0.13. Moreover, compared with 404 km, the longest distance reported so far, the transmission distance can theoretically be extended to 480 km and the key rate up to 5.4×10－4 bps in 404 km, with the same parameters.