2D atom localization in a four-level tripod system in laser fields
  We propose a scheme for two-dimensional (2D) atom localization in a four-level tripod system under an influence of two orthogonal standing-wave fields. Position information of the atom is retained in the atomic internal states by an additional probe field either of a standing or of a running wave. It is shown that the localization factors depend crucially on the atom-field coupling that results in such spatial structures of populations as spikes, craters and waves. We demonstrate a high-precision localization due to measurement of population in the upper state or in any ground state. 
Vladimir Ivanov, and Yuri Rozhdestvensky
physics.atom-ph