Multilevel systems: Simultaneously forbidden combination resonances

Multicolored coherent population trapping in a system using phase modulated fields

We demonstrate the simultaneous occurrence of coherent population trapping at a series of frequencies separated by modulation frequency of phase-modulated fields. The two arms of the system are coupled to two phase-modulated fields and the response of the atomic system to such fields is calculated nonperturbatively. A judicious choice of modulation characteristics allows one to selectively switch on or off the occurrence of coherent population trapping at specific frequencies. A new technique is developed to compute two-dimensional tridiagonal matrix equations. This generalized technique provides the vital methodology needed to calculate the response of such systems in the strong modulation regime and for arbitrary field strengths.