  Zero-photon catalysis (ZPC) introduces noiseless attenuation and can be
implemented by existing technologies in quantum key distribution (QKD)
protocols. In this paper, we present a ZPC-based eight-state
measurement-device-independent continuous-variable QKD (MDI-CV-QKD) combined
with discrete modulation and reverse reconciliation. This ZPC-involved
eight-state protocol shows better efficiency in terms of optimal modulation
variances, secret key rates, transmission distances, tolerable excess noises,
and reconciliation efficiency compared to the eight-state protocol without ZPC,
the four-state protocol without ZPC, and the four-state protocol with ZPC, at a
low signal-to-noise ratio (SNR).
