  Memory-assisted measurement-device-independent quantum key distribution
(MA-MDI-QKD) has recently been proposed as a possible intermediate step towards
the realization of quantum repeaters. Despite its relaxing some of the
requirements on quantum memories, the choice of memory in relation to the
layout of the setup and the protocol has a stark effect on our ability to beat
existing no-memory systems. Here, we investigate the suitability of nitrogen
vacancy (NV) centers, as quantum memories, in MA-MDI-QKD. We particularly show
that moderate cavity enhancement is required for NV centers if we want to
outperform no-memory QKD systems. Using system parameters mostly achievable by
today's state of the art, we then anticipate some total key rate advantage in
the distance range between 300 km and 500 km for cavity-enhanced NV centers.
Our analysis accounts for major sources of error including the dark current,
the channel loss, and the decoherence of the quantum memories.
