Bichromatic state-insensitive trapping of caesium atoms

M.M Metbulut,F Renzoni

doi:10.1080/09500340.2015.1073807

Abstract

State-insensitive dipole trapping of multilevel atoms can be achieved by an appropriate choice of the wavelength of the trapping laser, so that the interaction with the different transitions results in equal AC Stark shifts for the ground and excited states of interest. However, this approach is severely limited by the availability of coherent sources at the required wavelength and of appropriate power. This work investigates state-insensitive trapping of caesium atoms for which the required wavelength of 935.6 nm is inconvenient in terms of experimental realization. Bichromatic state-insensitive trapping is proposed to overcome the lack of suitable laser sources. We first consider pairs of laser wavelengths in the ratio 1:2 and 1:3, as obtained via second- and third-harmonic generation. We found that the wavelength combinations 931.8–1863.6 nm and 927.5–2782.5 nm are suitable for state-insensitive trapping of caesium atoms. In addition, we examine bichromatic state-insensitive trapping produced by pairs of laser wavelengths corresponding to currently available high-power lasers. These wavelength pairs were found to be in the range of 585–588 nm and 623–629 for one laser and 1064–1080 nm for the other.

Highlights

Dipole trapping is of great importance for cold atom research
The differential AC Stark shift between the ground and the excited states of the caesium atom was calculated for a variation of the trap laser wavelength up to a value λt = ±1.5 nm, while keeping the intensity ratio fixed for a combination of magic wavelengths of 623.5– 1064 nm
Bichromatic state-insensitive trapping of caesium atoms was investigated to overcome the problem of lack of sufficiently intense laser sources for free space monochromatic trapping

Summary

Introduction

Dipole trapping is of great importance for cold atom research. The ability to manipulate trapped neutral atoms plays an important role in many experiments in precision spectroscopy [1], optical clocks [2,3,4], quantum control [5] and quantum information processing [6]. By taking advantage of the multilevel structure of atoms, it was proposed to tune the trapping laser to a specific wavelength the so called magic wavelength – at which the differential light shift between the excited and the ground states of a particular transition vanishes This is the result of the interaction of the dipole trap laser field with all the different transitions of the multilevel atom, with relative weights determined by the laser detuning. Later in 2010, state-insensitive trapping of caesium atoms in free space was demonstrated [10] In this case the size and depth of the trap is severely limited by the power of available laser sources at the required wavelength. The effect of unwanted laser intensity and wavelength variations is discussed

Numerical results

Magic wavelength pairs corresponding to available high-power lasers

Effects of laser intensity and wavelength variations

Conclusion