Single-atom maser with an engineered circuit for population inversion

We present a blueprint for maser with single three-level transmon superconducting artificial atom. The system can be pumped coherently via two-photon process, and to achieve high population inversion, the relaxation rate of metastable state is increased an auxiliary low-$Q$ cavity coupled transition between excited states. show numerically that such operate both in intermediate-coupling regime super-Poissonian photon statistics strong-coupling regime, where sub-Poissonian. For former exhibits thresholdless behavior, latter there well-defined pumping threshold. A useful side effect resonator it allows overcome blockade pump, which would otherwise prevent population. Finally, we observe bistability steady-state Wigner function self-quenching some parameters.