  Recent experiments demonstrated the cooling of a microwave mode of a
high-quality dielectric resonator coupled to optically cooled nitrogen-vacancy
(NV) spins in diamond. Our recent theoretical study [arXiv:2110.10950] pointed
out the cooled NV spins can be used to realize cavity quantum electrodynamics
effects (C-QED) at room temperature. In this article, we propose to modify the
setup used in a recent diamond maser experiment [Nature 55, 493-496 (2018)],
which features a higher spin transition frequency, a lower spin-dephasing rate
and a stronger NV spins-resonator coupling, to realize better microwave mode
cooling and the room-temperature CQED effects. To describe more precisely the
optical spin cooling and the collective spin-resonator coupling, we extend the
standard Jaynes-Cumming model to account for the rich electronic and spin
levels of the NV centers. Our calculations show that for the proposed setup it
is possible to cool the microwave mode from $293$ K (room temperature) to $116$
K, which is about $72$ K lower than the previous records, and to study the
intriguing dynamics of the CQED effects under the weak-to-strong coupling
transition by varying the laser power. With simple modifications, our model can
be applied to, e.g., other solid-state spins or triplet spins of pentacene
molecules, and to investigate other effects, such as the operations of pulsed
and continuous-wave masing.
