Studies On Efficient Two-Dimensional Atom Localization In Multi-Level Atomic System

In recent years, much attention has been paid to efficient two-dimensional (2D) atom localization by researchers. In general, two orthogonal standing-wave fields instead of the standing-wave field along x direction in one-dimensional atom localization are applied to corresponding atomic transition. In this paper, we investigate efficient 2D atom localization via spontaneously generated coherence (SGC) and incoherent pump, via an external coherent magnetic field, or via the combination of Autler-Townes microscopy and the superposition of standing-wave fields. It is found that SGC, incoherent pump, coherent magnetic field and the asymmetric superposition of stand ing-wave fields play important roles in reducing the number of localization peaks and increasing the probability of finding the atom in 2D space. Three schemes for 2D atom localization have been proposed as following:1. Efficient 2D atom localization via SGC and incoherent pump. In this scheme, in the case of a weak probe field, when an incoherent pump is used to pump a closed three-level △-typed atomic system, the SGC effect can be reserved. Due to the combination of incoherent pump and SGC, the optical properties of the system depend on the phases of the applied fields. Because of the position dependent atom-field interaction, when passing through the orthogonal standing-wave fields, the position of the atom in 2D space can be achieved by measuring the probe absorption and gain. We can realize 2D atom localization with high precision and high spatial-resolution and the detecting probability of the atom in unit wavelength domain can reach 100%.2.2D sub-half-wavelength atom localization via an external coherent magnetic field. In the closed three-level △-typed atomic system, the transition between two low states is electric dipole forbidden while magnetic dipole allowed. An external coherent magnetic field is applied to the transition to form a closed loop configuration. Due to the spatial modulation of the standing-wave fields, in the case of three photon resonance and in the limit of the weak probe and magnetic field, the distribution of the population in the excited state, which is sensitive to the collective phase of the probe and standing-wave fields, depends on the spatial position. In the presence of the coherent magnetic field, we can achieve single localization peak structure and localize the atom at a particular position in the x-y plane.3. Localization of a three-level cascade-type atom via the combination of the Autler-Townes microscopy and the superposition of standing-wave fields. If we simply choose two orthogonal standing-wave fields, the Autler-Townes microscopy in the three-level cascade-type atom displays a symmetrical structure and the probability of finding the atom is only 50%. We use the superposition of the standing-wave fields, which means that each of the standing-wave fields, i.e., along the x and y directions, is again the superposition of two standing-wave fields along the corresponding directions. When the two standing-wave fields along the same direction have different values of the wavelength and phase (asymmetric superposition of standing-wave fields), Autler-Townes microscopy shows an asymmetric structure. We can reduce the number of the atom localization peaks and improve the detecting probability of the atom to 100% via properly adjusting the parameters of the system.