Coherent population trapping , quantum system

The three-level saturation spectroscopy of A- and V-level configurations flourished in the subsequent years and led to the discovery of munerous new effects, such as coherent population trapping (Arimondo 1996), electromagnetically induced transparency (Harris 1997), and lasing without population inversion (Kocharovskaya 1992). These effects are beyond the scope of the present book. The control of quantum coherence and interference in laser-driven three-level systems has been treated in detail in the excellent reviews cited above. 

The coherent population-trapping effect is manifested in various domains of atomic and laser physics (see Section 4.4.2). Let a quantum mechanical system described by a nonperturbed operator Hq be placed in an external field. Its interaction with the field is described by an operator V. In this case, the temporal evolution of the state t) of the system in the interaction representation is described by the Schrodinger equation as... 

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