Using three-wave mixing to achieve ultra-narrow masing with superconducting quantum circuits

The laser has proven itself as a highly useful tool for its ability to create coherent signals from incoherent drives. In this talk, we will demonstrate how we couple a single transmon qubit to a high-Q superconducting cavity to create a Josephson junction-based micro-maser. Our experiment utilizes parametric three-wave coupling between our qubit and a SNAIL coupler, which we use to invert the qubit population to its excited state and irreversibly erase previous phase information of the system. Once in the excited state, the qubit resonantly exchanges energy with the high-Q cavity. This continuous process occurs because the qubit population is continuously inverted by the parametric drive as light builds up in the maser cavity. We will demonstrate our ability to approach the standard Schawlow-Townes limit on maser linewidth with a high photon number. We will also discuss the utilization of nonlinearity in the qubit-cavity and cavity-transmission line couplings to circumvent the standard Schawlow-Townes limit to realize an even narrower quantum light source.