Nonlinear magneto-optical effects and quantum coherences in cold rubidium atoms in an optical dipole trap

Abstract

Summary form only given. We report on our experiments on nonlinear magneto-optical effects in laser-cooled, near-degenerate rubidium samples. Atoms are laser-cooled and subsequently transferred to the crossed-beam optical dipole trap (ODT), formed by a tight focusing of 1560-nm laser beams. The trap not only provides long relaxation time but also allows us to investigate the quantum degeneracy regime. Moreover, the tight confinement of atoms enables magnetic field probing with a high spatial resolution of a few tens of micrometers.Interaction of atoms with a near-resonant, linearly polarized light leads to an effective creation of long-lived ground-state Zeeman coherences, which is observed through the nonlinear Faraday effect [1] or free induction decay signals of the Larmor precession. Our previous experiments proved that high rotation angles of a few degrees (Fig. 1a) and coherence lifetimes of a few milliseconds (Fig. 1b) can be achieved with cold atoms released from the magneto-optical trap (MOT) in a simple magnetic shielding [2]. In the present work, we intend to keep atoms in a far off-resonant ODT, which enables much longer observation times. Our goal is to study coherence effects in the temperatures down to the limit of quantum degeneracy, i.e., a Bose-Einstein condensate.Application of these effects to the precision magnetometry and its potential limits are presented. By employing the amplitude-modulated optical rotation we are able to measure high (geophysical range) magnetic fields [2-3]. Moreover, Zeeman coherences form a versatile tool for studying superposition states which are vital fundamental atomic physics and quantum information. In this work, we demonstrate the dynamics of coherent superposition states under the influence of laser and magnetic fields. Finally, we discuss a new scheme utilizing chirped pulses to instantaneously create maximum allowed Zeeman coherences [4].