Light Amplification without Inversion from Hybrid Quantum Dot–Resonator Circuit: Floquet Nonequilibrium Green's Function Approach

Herein, a new mechanism of steady‐state light amplification without inversion from a hybrid quantum dot circuit coupled to a single mode of electromagnetic resonator is theoretically investigated. Hybrid quantum dot circuit consists of a single‐level quantum dot which is connected weakly to one normal metal electrode and strongly to one superconducting electrode. Using the Floquet nonequilibrium Green's function technique, it is shown that the gain originates from the Andreev reflection processes at proper gate voltages when the bias voltage exceeds a certain threshold. Also, it is found that the inversionless light amplification is mediated by spin transitions between Andreev and Floquet–Andreev bound states in the superconducting energy gap.