Efficient two-dimensional sub-wavelength atom localisation via probe absorption in a four-level Λ-shaped atomic system

Two-dimensional (2D) atom localisation of a four-level Λ-shaped atomic system with a nearly hyper-fine doublet interacting with two orthogonal standing-wave fields is investigated. The spatial information of a moving atom in xy plane is obtained by measuring the probe field absorption. The effect of quantum interference on two-dimensional atom localisation is described. The intensity of standing-waves and the detuning of the probe and standing-wave fields are found to strongly affect the two-dimensional atom localisation that lead to different spatial distribution patterns.