The Localization Of The Moving Three-Level Atom

In recent years, much attention has been paid to the subwavelength localization of an atom using a standing-wave optical field. The optical methods provide better spatial resolution and have their potential applications to many areas of optical manipulations of atomic degrees of freedom. Among other things, there are laser cooling, Bose-Einstein condensation,and atom lithography, and measurement of the center-of-mass wave function of moving atoms. Earlier schemes for the localization include the measurement of the phase shift of either the standing wave or the atomic dipole due to the interaction of the atom with the standing wave field, the entanglement between the atom's position and its internal states, and the resonance imaging methods. More recently, the detection of the Autler-Townes spectra (absorption spectra and spontaneous emission spectra) have been used for the atom localization. In this thesis, we presented two new localization scheme via absorption spectra and resonance fluorescence spectra.1. Localization of a three-level cascade atom via resonant absorption. We show that it is possible to localize a three-level cascade atom under the resonance condition when it passes through a standing-wave field. The localization peaks appear at the nodes of the standing-wave field, the detecting probability is 50% in the subwavelength domain, and the peaks are narrower on the resonance than the off-resonance. The absorption is the same as that in the usual two-level medium at the nodes and is greatly suppressed outside the nodes due to the Autler-Townes splitting. This is in sharp contrast to the A scheme, in which the localization is impossible under the same resonance condition due to the depletion of population of the initial state by the probe field at the nodes and the electromagnetically induced transparency outside the nodes.2. Sub-half-wavelength atom localization via coherence-controlled resonance fluorescence. It is possible to localize an atom in a regime of half-wavelength by detecting coherence-controlled resonance fluorescence. The three-level atom in the A configuration is considered. Two metastable states are so separated from each other that the fluorescence spectra on the different transitions are not overlapped. Two dipole-allowed transitions and one dipole-forbidden transition are driven by a standing-wave laser field, a travelling-wave laser field, and a microwave field, respectively. The fluorescence spectrum is dependent not only on the position but also on the collective phase of all applied fields. When the phase is varied and the fluorescence photons are detected, 50% probability is achieved in a half-wavelength region. This scheme is as efficient as previous ones based on coherence controlled Autler-Townes spectra.