Title: Portable diamond maser with reduced magnetic field through orientation

Abstract: Masers have the potential to transform medical sensing and boost qubit readout detection due to their superb low-noise amplification. The negatively-charged nitrogen vacancy (NV-) diamond maser is the only continuous-wave solid-state maser discovered at room temperature, however it suffers from requiring large and bulky magnets which prevent its more widespread use. We present a significant reduction in size of the entire diamond maser using a much lighter and small-footprint electromagnet, reducing the weight from an immovable 2000 kilograms to a portable 30 kilograms. We achieve a maximum maser output power near -80 dBm, ten times higher than the first implementation, and have discovered techniques to reduce the magnetic field strength required for masing by precise manipulation of the spin orientation. With the diamond maser now shrunk to a size that can fit on a lab benchtop, we have brought continuous-wave room temperature masers away from the confines of research laboratories and closer to transforming readouts in quantum computing, frequency standards and quantum-limited medical sensing.