Two single-state semi-quantum secure direct communication protocols based on single photons

Abstract

Semi-quantum protocol is a hot topic in quantum cryptography. One of the original motivational reasons to study semi-quantum protocol is to better understand “how quantum” a protocol needs to be in order to gain an advantage over its classical counterpart. Semi-quantum secure direct communication (SQSDC) is an important branch of the semi-quantum protocol, which makes it possible to directly transfer large amounts of data between quantum participant and classical participant without need to share the secret key in advance. In this paper, we propose two new SQSDC protocols based on single photons to study how to reduce the quantum resource requirements of both quantum participant and classical participant. In both protocols, the classical participant requires neither quantum memory or quantum delay lines. We first propose in the first protocol that the quantum participant only need to prepare single-state qubits in the preparation phase, which is different from previous SQSDC protocols. Then we propose in the second protocol that quantum participant can accomplish the same work as the first one even without quantum memory. Efficiency analysis shows that the first protocol is more efficient than some protocol, and the second one can save more quantum resources at the expense of some efficiency. Compared with the existing SQSDC protocols based on single photons, both protocols can use fewer quantum states or quantum resource requirements than other protocols. Finally, we analyze the security of both protocols.