Spectral line narrowing via spontaneously generated coherence in quantum dot molecules

We theoretically demonstrate that it is possible to simulate spontaneously generated coherence in an asymmetric double quantum dot system, a quantum dot molecule. With the tunneling coupling, the system emulates to large degree a three-level system with quantum interference and the fluorescence spectrum can display ultranarrow lines. In our system the coupling field is not necessary and the degree of quantum interference can be controlled. The dressed states for this system are identified, and the spectral features are interpreted in terms of transitions among these dressed states. The system studied here is more practical and can permit the observation of spontaneously generated coherence without the need for closely lying levels and parallel dipole moments.