ATOMIC COHERENCE IN LASERS AND MASERS

We demonstrate the effect of atomic coherence on the generic example of two lossless micromasers coupled in series by a common pump beam of excited two-level atoms. The fields are studied via conditional measurements on the final state of the atoms. We consider the two simplest sequences: in the energy preserving (transferring) scheme we require each atom to be detected in its upper (lower) state. Due to the two paths that the atoms can follow to reach the same final state correlation between the two macroscopically separated fields can arise. We discuss a scheme which leads to the generation of entangled trapping states of the two fields of the form, \n, n + M] +/- \n + M, n], starting from number states \n, n]. Starting from initial coherent states arbitrary steady-state superpositions of the two fields can be generated by switching from the energy transferring to the preserving scheme at an optimum number of atoms. In the absence of dissipations, both methods can produce steady-state coherent superpositions of arbitrary number states of two macroscopically separated fields (nonlocal 'Schrodinger-cats'). A scheme is discussed where entanglement can be transferred from the fields to two atomic beams. finally, we briefly discuss the effect of injected atomic coherence on lasers.