My new paper in npj Quantum Information on cavity quantum electrodynamics using masers is available free (open access) here:
Room-temperature cavity quantum electrodynamics with strongly coupled Dicke states
In this work, we managed to achieve strong-coupling at room-temperature with a photo-excited spin-ensemble. Similar studies have been presented previously with ensembles of paramagnetic ions, but this is the first time an almost pure collective quantum state had been initialised. Of the \(10^{\sf 15}\) pentacene molecules, over 90% were prepared in the excited state.
This was a fun paper. Realising we were operating in the strong-coupling regime of cavity quantum electrodynamics, for me, was a milestone.