Coherence Effects in Cold Atoms

Dr Wojciech Gawlik

Institute of Physics, Jagiellonian University, Kraków, Poland

3:30 pm, Friday, 14 August 2015, EN102 Lecture Theatre (EN Building), Hawthorn

I will report on experiments with cold atoms performed in the Jagiellonian University. The experiments concentrate on nonlinear magneto-optical effects in laser-cooled, rubidium samples. Interaction of atoms with a near-resonant, linearly polarized light leads to an efficent creation of long-lived ground-state Zeeman coherences, which is observed through the nonlinear Faraday effect or free induction decay signals of the Larmor precession.
The experiments showed that high rotation angles of a few degrees and coherence lifetimes of a few milliseconds are achieved in mG fields with cold atoms released from MOT in a simple magnetic shielding. The coherence signal observed via the nonlinear Faraday rotation allows magnetometric diagnostics of the local magnetic field inside the vacuum system, including the induced eddy currents and external oscillating fields. The magnetic field inhomogeneity and finite lifetime of atomic sample are the main limitations of the coherence time. Significant enhancement of the coherence and polarization lifetimes can be achieved by application of stroboscopic technique and allowing relaxation in the dark.
In the next-generation setup, we keep atoms in a far off-resonant optical dipole trap (ODT) inside an improved magnetic shield. The ODT provides long relaxation time and large on-axis optical depth, which result in the improved sensitivity to the magnetic field. Moreover, the tight confinement of atoms enables magnetic field probing with a spatial resolution of a few tens of micrometers.