Masing with a single artificial superconducting atom and parametric controls

Superconducting quantum circuits can be flexibly engineered to allow us to explore quantum optics topics such as masing and its quantum limits. In this talk, we will present such an exploration of a maser based on a superconducting quantum circuit system comprised of a deliberately low-Q SNAIL and a flux-tunable transmon, which form an artificial three-level atom, and a high-Q cavity. By designing the decay rate of the SNAIL to be much larger than the qubit T1 and the exchange rate between the resonant qubit and cavity, we can invert the qubit population with the application of a parametric sum-frequency drive on the SNAIL which couples it to the qubit. Together, these processes result in photon accumulation within the cavity, ultimately leading to masing. During the masing process, we observe a narrowing of the maser linewidth from 6.4 kHz to 54 Hz, which we can observe directly in the time domain. We also observe an apparent two-photon swapping between the qubit and cavity, offering masing at an unexpected set of bias conditions, which we present and explain via simulations based on the master equation for the system. In addition, we will explore injection locking on our masing, which can further narrow the linewidth of the maser. We will also discuss prospects for extending the system with a low-noise coupler for qubit-cavity and cavity-output coupling, which has been proposed as a method to surpass the standard Schawlow-Townes limit on maser and laser linewidth