一步量子安全直接通信

One-step quantum secure direct communication

量子安全直接通信(QSDC)是通信双方不需要事先共享密钥,直接利用量子信道传输机密信息的一种新型保密通信模式.传统QSDC方案需要在量子信道中分发两轮光子.本文利用极化-空间超纠缠态设计了一种新型的一步QSDC方案,只需在量子信道中分发一轮光子.因此,该方案可简化实验操作并降低信息错误,实现双向通信,且在理论上具有绝对安全性.此外,通过分发一对超纠缠光子能传递2比特的信息,该方案具有较高的通信效率.在极化和空间自由度的纠缠保真度为0.98的情况下,该方案的最大通信距离约为216 km.QSDC也可用于远距离分发密钥,与传统的基于纠缠的量子密钥分发(QKD)方案相比,该方案在150 km的通信距离的密钥产生率约为QKD的2.5倍.而且,借助于未来的量子中继技术,采用该方案有望实现任意长距离的安全通信.

Quantum secure direct communication(QSDC)attracts much attention for it can transmit secret messages directly without sharing a key.In this article,we propose a one-step QSDC protocol,which only requires to distribute polarization-spatial-mode hyperentanglement for one round.In this QSDC protocol,the eavesdropper cannot obtain any message,so that this protocol is unconditionally secure in principle.This protocol is a two-way quantum communication and has high capacity for it can transmit two bits of secret messages with one pair of hyperentanglement.With entanglement fidelities of both polarization and spatial-mode degrees of freedom being 0.98,the maximal communication distance of this onestep QSDC can reach about 216 km.QSDC can also be used to generate the key.In this regard,the key generation rate is estimated about 2.5 times of that in the entanglement-based QKD with the communication distance of 150 km.With the help of future quantum repeaters,this QSDC protocol can provide unconditionally secure communication over arbitrarily long distance.