Semiconductor double quantum dot micromaser

The coherent generation of light, from masers to lasers, relies upon the
specific structure of the individual emitters that lead to gain. Devices
operating as lasers in the few-emitter limit provide opportunities for
understanding quantum coherent phenomena, from THz sources to quantum
communication. Here we demonstrate a maser that is driven by single electron
tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain
medium and are placed inside of a high quality factor microwave cavity. We
verify maser action by comparing the statistics of the emitted microwave field
above and below the maser threshold.