Quantum mechanics

Quantum key distribution

Computer security

Operating system

Computer science

Protocol (science)

Computer network

Physical chemistry

Polarization (electrochemistry)

Alternative medicine

Physics

Quantum entanglement

Mathematics

Quantum information science

Quantum

Combinatorics

Medicine

Chemistry

Topology (electrical circuits)

Mode (computer interface)

Pathology

Key (lock)

Science Bulletin

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 one-step 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.

One-step quantum secure direct communication