LAUSR

We propose a scheme of double-scanning 4-intensity MDI-QKD protocol with the modified coherent state (MCS) sources. The MCS sources can be characterized by two positive parameters, ξ and c. In all prior works, c was set to be the same for all sources. We show that the source parameter c can be different for the sources in the X basis and those in the Z basis. Numerical results show that removing such a constraint can greatly improve the key rates of the protocol with MCS sources. In the typical experiment conditions, comparing with the key rates of WCS sources, the key rates of MCS sources can be improved by several orders of magnitude, and the secure distance is improved by about 40 km. Our results show that MCS sources have the potential to improve the practicality of the MDI-QKD protocol.