A Josephson junction-based maser using three-wave mixing

Lasers are a ubiquitous tool throughout physics because they allow us to create highly coherent signals from incoherent drives. In this talk, we will introduce a Josephson junction-based micro-maser made by coupling a single superconducting transmon to a high-Q superconducting cavity, as well as a Superconducting Nonlinear Asymmetric Inductive eLement (SNAIL) mode. The qubit-SNAIL interaction is controlled via a parametric two-photon gain process, which inverts the qubit population to its first excited state via the SNAIL’s short lifetime and the transmon’s anharmonicity. The qubit in turn couples resonantly to a cavity which accumulates photons and mases.  We will demonstrate an experimental realization of this system, including population inversion and the relationship between parametric drive strength and masing bandwidth. Additionally, we will discuss the prospects for further extending the system with engineered qubit-cavity and cavity-output couplings which have been recently proposed as a way to circumvent the standard Schawlow-Townes limit on maser/laser linewidth [Liu, et al., Nat. Comm (2021)].