Disentanglement of Source and Target and the Laser Quantum State

Disentanglement of a laser source from its target qubit is proposed as a criterion establishing the laser quantum state as a coherent state. It is shown that the source-target density operator has a unique factorization in coherent states when the environmental record monitoring laser pump quanta is ignored. The source-target state conditioned upon the complete environmental record is entangled, though, as a state of known total quanta number (source plus target).

Figure 1

Schematic of the scattering scenario for a laser source illuminating a target qubit.