Quantum interference and quantum-Zeno effect in amplification without inversion

We analyze amplification without inversion (AWI) in different
homogeneously broadened closed three-level systems in the framework of
both density-matrix and quantum-jump formalisms. With the density-matrix
formalism we study the nature of quantum interference in these systems;
determine analytically the condition for AWI and locate the position of
maxima and minima in the probe absorption spectrum. Within the
quantum-jump formalism we calculate the relative probabilities of the
various physical processes responsible for probe field amplification and
absorption, and analyze the role of the quantum-Zeno effect in AWI. The
result is that AWI in the h and p schemes is due to one-photon processes
while for V and Lambda schemes are due to two-photon processes. We also
show that AWI in V and h schemes always occurs in the quantum-Zeno
regime, while this regime is not necessary for AWI in the Lambda and p
schemes.