Resonant fluorescence of a bichromatically driven three-level atom with the electron shelving effect

The electron shelving effect significantly improves the control accuracy of medium energy level transitions, enabling high-sensitivity fluorescence signal detection in precision spectroscopy and quantum metrology and thus allowing a more precise investigation of the microstructure and dynamical behavior of the medium. Here, we investigate theoretically the fluorescence properties of bichromatically driven three-level atoms with electron shelving effect under strong coupling conditions. The physical process by which the electron shelving effect leads to the appearance of two types of peaks in the central peaks of multiple Mollow triplets is explored. This phenomenon is attributed to the different orientations of electric dipole moments in fluorescence emission process caused by a nonresonant weak field. Due to the disappearance of the central broad peak of the central Mollow triplet caused by the quantum interference, the pure sharp peak survives completely induced by the electron shelving effect. The physical picture of the two-mode squeezing effect in out-of-phase quadrature noise spectra originating from the asymmetrical fluorescence operators induced by the nonresonant weak field is revealed. Moreover, the frequency range and degree of two-mode squeezing can be improved by appropriately increasing the Rabi frequency of the weak field. These results not only are helpful for realizing the electron shelving effect experiment in polychromatic strong-coupling systems but also provide a scheme for developing nonclassical spectroscopy and quantum precision measurement based on the electron shelving effect.