Long-distance measurement-device–independent quantum secure direct communication

Abstract

Quantum secure direct communication enables a direct message exchange over a quantum channel without any key generation in advance. Here we present a feasible protocol for long-distance measurement-device–independent quantum secure direct communication. The secure distance is increased by using ancillary entangled photon-pair sources and relay nodes. Meanwhile, its security is independent from measurement devices, which eliminates the potential loophole for eavesdropping in the detection systems. Moreover, this protocol can be implemented with linear optical devices and single-photon detectors.