The standard quantum limit on laser/maser linewidth was first introduced by Schawlow and Townes in 1958 and has remained essentially unchallenged until today. I will argue that using the standard components of superconducting quantum computers it is possible to construct a maser that is considerably narrower than the standard quantum limit. Indeed, we expect our design to be narrower than the standard quantum limit by a factor proportional to the number of photons in the maser cavity. Thus, our maser design bridges the gap between the standard quantum limit and the ultimate Heisenberg limit (which is narrower than the standard quantum limit by a factor proportional to the number of photons in the laser cavity squared). Our maser could function as an ultra-coherent, cryogenic light source for microwave quantum information experiments. Further, the maser contains highly squeezed light which could be an important resource for continuous variable/linear optical quantum computing, readout of quantum states in superconducting quantum computers, quantum metrology, and quantum communication.
