Masers are the lowest-noise microwave amplifiers known, with applications wherever a weak signal exists in a potentially noisy environment [1]. However, though masers were first discovered in the 1950s their use has so far been limited to niche applications in radio astronomy and deep-space communications due to the ultrahigh vacuums and cryogenic temperatures required by conventional masers. The recent discovery [2] that ensembles of nitrogen-vacancy (NV) centres in diamond can be used as gain media for masers capable of operating in ambient conditions thus opens up a vast frontier of new applications in telecommunications, medical imaging and quantum sensing. In order to realise these new applications, the diamond maser will need to be developed into a miniaturised, portable form compatible with existing standards in microwave devices. In particular, first-generation diamond masers are limited by bulky electromagnets (typically used for electron paramagnetic resonance spectroscopy) required to achieve sufficiently homogeneous magnetic fields to allow them to operate.

Here we discuss strategies for reducing this reliance on ultra-homogeneous magnetic fields by optimising the material parameters NV-enriched diamond [3], in particular by tuning the concentration of NV centres and controlling the isotopic content of the carbon lattice. We conclude by discussing recent progress in the construction of miniaturised maser devices.

[1] Arroo et al., Perspective on room-temperature solid-state masers, Appl. Phys. Lett. 119, 140502 (2021)
[2] Breeze et al., Continuous-wave room-temperature diamond maser, Nature 555, 493–496 (2018)
[3] Wen et al., Exploring the spin dynamics of a room-temperature diamond maser using an extended rate equation model, J. Appl. Phys. 134, 194501 (2023)