  By strongly driving a cyclic-transition three-level artificial atom,
demonstrated by such as a flux-based superconducting circuit, we show that
coherent microwave signals can be excited along a coupled one-dimensional
transmission line. Typically, the intensity of the generated microwave is
tunable via properly adjusting the Rabi frequencies of the applied
strong-driving fields or introducing a probe field with the same frequency. In
practice, the system proposed here could work as an on-chip quantum device with
controllable atom-photon interaction to implement a total-reflecting mirror or
switch for the propagating probe field.
