Single-artificial-atom lasing using a voltage-biased superconducting charge qubit

TL;DR

This paper analyzes a single artificial atom coupled to a cavity, demonstrating conditions for lasing and suppression in a superconducting charge qubit system, with analytic and numerical results matching well.

Contribution

It provides analytic expressions for lasing suppression conditions and cavity states in a superconducting artificial-atom laser, extending understanding of inverted relaxation effects.

Findings

Lasing can be suppressed if relaxation rate exceeds a threshold.

Analytic formulas accurately predict lasing and suppression regimes.

Numerical results agree with semiclassical calculations.

Abstract

We consider a system composed of a single artificial atom coupled to a cavity mode. The artificial atom is biased such that the most dominant relaxation process in the system takes the atom from its ground state to its excited state, thus ensuring population inversion. A recent experimental manifestation of this situation was achieved using a voltage-biased superconducting charge qubit. Even under the condition of `inverted relaxation', lasing action can be suppressed if the `relaxation' rate is larger than a certain threshold value. Using simple transition-rate arguments and a semiclassical calculation, we derive analytic expressions for the lasing suppression condition and the state of the cavity in both the lasing and suppressed-lasing regimes. The results of numerical calculations agree very well with the analytically derived results. We start by analyzing a simplified two-level-atom model, and we then analyze a three-level-atom model that should describe accurately the recently realized superconducting artificial-atom laser.