  The discrete modulation can make up for the shortage of transmission distance
in measurement-device-independent continuous-variable quantum key distribution
(MDI-CVQKD) that has an unique advantage against all side-channel attacks but
also challenging for the further performance improvement. Here we suggest a
quantum catalysis (QC) approach for enhancing the performance of the
discrete-modulated (DM) MDI-CVQKD in terms of the achievable secret key rate
and lengthening the maximal transmission distance. The numerical simulation
results show that the QC-based MDI-CVQKD with discrete modulation that involves
a zero-photon catalysis (ZPC) operation can not only obtain a higher secret key
rate than the original DM protocol, but also contributes to the reasonable
increase of the corresponding optimal variance. As for the extreme asymmetric
and symmetric cases, the secret key rate and maximal transmission distance of
the ZPC-involved DM MDI-CVQKD system can be further improved under the same
parameters. This approach enables the system to tolerate lower reconciliation
efficiency, which will promote the practical implementations with state-of-art
technology.
