Spontaneous emission spectra from a five-level atom with a loop structure

The spontaneous emission property of a five-level atom with a loop structure driven by three optical fields and a microwave field is intensively studied. Several quantum interference effects can be observed in the spontaneous emission spectra, such as spectral-line narrowing, spectral-line enhancement, spectral-line suppression, partial cancellation and fluorescence quenching. The number of emission peaks, the positions of dark lines can be controlled by varying the intensities of driving fields or the phase of the microwave field coupling the two lower levels in the atomic system. Furthermore, since no rigorous conditions are required, the expected phenomena may easily be achieved experimentally in atomic systems.