Efficient two-dimensional atom localization via phase-sensitive absorption and gain spectra in a cycle-configuration four-level atomic system

A scheme of two-dimensional atom localization is proposed based on the phase-sensitive probe absorption and gain in a four-level atomic system with a closed-loop configuration. Due to the spatially dependent atom-field interaction, the position probability distribution of the atom can be directly determined by measuring the resulting absorption and gain spectra of the weak probe laser field. It is found that the phase-sensitive property of the atomic system significantly improves the localization behavior. Especially the maximal probability of finding the atom at a particular position within the sub-wavelength domain of the standing waves can arrive at unity by appropriate choice of the system parameters.