One-step device-independent quantum secure direct communication

Device-independent quantum secure direct communication (DI-QSDC) can relax the security assumptions about the devices’ internal working, and effectively enhance QSDC’s security. In this paper, we put forward the first hyperentanglement-based one-step DI-QSDC protocol. In this protocol, the communication parties adopt the nonlocal hyperentanglement-assisted complete Bell state analysis, which enables the photons to transmit in the quantum channel for only one round. The one-step DI-QSDC can directly transmit 2 bits of messages by a hyperentangled photon pair, and is unconditionally secure in theory. Compared with the original DI-QSDC protocol (Sci. Bull. 65, 12 (2020)), the one-step DI-QSDC protocol can simplify the experiment and reduce the message loss. In particular, with the help of the hyperentanglement heralded amplification and the hyperentanglement purification, the message loss and the message error caused by the channel noise can be completely eliminated, and the communication distance can be largely extended. By using the photon source with a repetition rate of 10 GHz, the one-step DI-QSDC’s secret message capacity under 50 km communication distance achieves about 7 bit/s with the initial fidelity in each degree of freedom of 0.8. Combined with the quantum repeater, it is possible for researchers to realize the one-step DI-QSDC with an arbitrarily long distance.