We propose a tunable on-chip micromaser using a superconducting quantum
circuit (SQC). By taking advantage of externally controllable state
transitions, a state population inversion can be achieved and preserved for the
two working levels of the SQC and, when needed, the SQC can generate a single
photon. We can regularly repeat these processes in each cycle when the
previously generated photon in the cavity is decaying, so that a periodic
sequence of single photons can be produced persistently. This provides a
controllable way for implementing a persistent single-photon source on a
microelectronic chip.Comment: 8 pages, 4 figure