Quantum secure direct communication via circle-based two-step quantum walks

Quantum secure direct communication (QSDC) enables the secure transmission of private messages directly via a quantum channel with no necessity for establishing a secret key. In this paper, we suggest a QSDC scheme via two-step quantum walks (QWs) on a circle. To be specific, the first-step QW is designed for determinately producing the required entangled states as quantum channel on account of appropriate coin operators and conditional shift operators between position and coin spaces, which avoids preparing the precursory entangled states. The second-step QW, in company with the produced entangled states and one single-particle state, is applied to transmit secret messages by utilizing QW-based quantum teleportation assisted with local measurements embodied with two projective measurements instead of one Bell-state joint measurement in existing QSDC protocols, which implies a simpler implementation. Security analyses and discussions exhibit that the raised QSDC scheme is resistant to intercept-and-resend attacks and that it has better performance referring to the protocol's success probability.