Measurement-free mediated semi-quantum key distribution protocol based on single-particle states

A novel measurement-free mediated semi-quantum key distribution (MSQKD) protocol is proposed based on single-particle states. It enables two classical users to establish a secret key with the assistance of a third party. This protocol simplifies the third party’s role to solely generating qubits in X-basis and conducting Bell measurements. A distinctive feature of this protocol is the efficient grouping and reordering of qubits by the classical users with a minimum of three delay lines. Security analyses demonstrate that the protocol can withstand various attack strategies, including collective attack, measurement attack, fake state attack, and modification attack. The noise tolerance is given by deriving a lower bound of the protocol’s key rate in the asymptotic scenario. Simulations on the IBM Quantum Experience platform are conducted to illustrate the feasibility of this protocol. Compared with existing MSQKD protocols, the proposed protocol consumes fewer quantum resources and achieves a qubit efficiency of 1/8.