A quantum theory of a two and three-level laser with injected atomic coherence is developed by using a density operator method, to the best of our knowledge, for the first time. The initial atomic coherence plays an essential role. At steady state, the equation of motion for the density operator yields to exhibit laser without inversion and a phase locking but no threshold for the laser fie...

a quantum theory of a two and three-level laser with injected atomic coherence is developed by using a density operator method, to the best of our knowledge, for the first time. the initial atomic coherence plays an essential role. at steady state, the equation of motion for the density operator yields to exhibit laser without inversion and a phase locking but no threshold for the laser field. ...

In this paper, we clarify the applicability of the super operator technique for describing the dissipative quantum dynamics of a system consists of two qubits coupled with a thermal bath at finite temperature. By using super operator technique, we solve the master equation and find the matrix elements of the density operator. Considering the qubits to be initially prepared in a general mixed st...