Population trapping in ruby

Population trapping in the ground state spin sublevels of Cr3+ in ruby at l iquid helium temperature is considered. It is proposed to excite the R-1-tr ansition by a bichromatic laser beam with an optical frequency difference m atching the ground state spin sublevels splitting. If the excitation is str ong enough to decouple Cr3+ from its environment, responsible for dephasing , an appreciable amount of the population is trapped in a particular superp osition of the spin sublevels. This superposition state does not interact w ith the laser beam because of the destructive interference of the quantum p aths constituting the transition. Population trapping can be detected by th e reduced luminescence from the excited state and by the magnetization ring ing originating from the ground state spin coherence.