Optical dipole trap without inhomogeneous ac stark broadening

Frank Markert, P Würtz, Andreas Koglbauer +3 more

We have measured the ac-Stark shift of the 14 D 5/2 Rydberg state of rubidium 87 in an optical dipole trap formed by a focused CO 2 laser. We found good quantitative agreement of the result with the model of a free electron experiencing a ponderomotive potential in the light field. In order to reproduce the observed spectra, we take into account the broadening of the Rydberg state due to photoionization. The extracted cross section is compatible with previous measurements on neighboring Rydberg states.

Rudolf Grimm, Matthias Weidemüller, Yuri B. Ovchinnikov

Jai Min Choi, D. Cho

We propose a way to eliminate the inhomogeneous broadening for a ground-state hyperfine transition of an alkali metal atom in an optical trap by using a properly polarized trapping field. The ac Stark shift contribution from the vector polarizability has opposite sign for a pair of ground hyperfine levels. It can be used to eliminate the inhomogeneous broadening from the difference in the scalar polarizbilities due to the hyperfine splitting. The size of the vector term is determined by the polarization state of the trapping field, and by controlling the polarization tightly one can achieve a very narrow linewidth. We estimate required tolerance in the polarization control to achieve 1-Hz linewidth for a specific case of a cesium atom. This proposal has significant implications for an electric dipole moment measurement using cesium atoms and quantum information processing using an optical lattice.

Galina A. Nemova

Kavish Bhardwaj, Surjya Prakash Ram, S Singh +2 more

Abstract In this work, the effect of AC-Stark shift of atomic energy levels in an optical dipole trap (ODT) on in situ absorption imaging of the trapped atoms has been investigated. The Stark shift of various energy levels of 87 Rb atoms relevant for trapping in the optical dipole trap (ODT) has been calculated. The spatially varying AC-Stark shift of energy levels due to ODT beam results in position dependent absorption cross-section of the atom at the absorption probe laser wavelength, which significantly modifies the measured optical density (OD) of the trapped atom cloud during the in situ absorption imaging. We have estimated the number of atoms trapped in the ODT taking AC-Stark shift into account. The estimated numbers are found to be higher at higher ODT beam power, making a qualitative agreement with larger trap depth at higher ODT beam power. This work can be particularly useful in estimating the in situ loss rate of atoms from the trap during the evaporative cooling of the trapped atom cloud.

Gautam Ramola