Observation of spontaneously generated coherence on absorption in rubidium atomic beam

Abstract

We report the experimental observation of the effect of spontaneously generated coherence on absorption without the rigorous requirement of close-lying levels. The experiments are studied in both a four-level N-type and a four-level inverted-Y-type atomic system in a rubidium atomic beam. With the coupling and controlling field, the N-type system is equivalent to a system with three closely upper levels coupled to one lower level by the same vacuum modes. The quantum interference can induce two prominent and nearly transparent holes where the slope of the refractive index is very steep. This special situation could allow the simultaneous propagation of two weak pulses with different frequencies. When we tune the wavelength of the controlling field, the N-type system turns to be the inverted-Y atomic system. Under the two-photon resonance condition, the system is equivalent to a V-type system with two closely upper levels, and the interference can reduce one broad transparency window in the middle of the absorption spectrum. Besides we can control the number of the spontaneously decay channels by the detuning of the controlling field, thus the effect of spontaneously generated coherence can exist in three or two closely space levels.