Planar structures for two-color, single-beam magneto-optical traps

authored by
Saskia Bondza
supervised by
Christian Lisdat

The exploration of quantum physics has heralded a new era of quantum sensors with improved measurement precision compared to conventional systems. Quantum sensors based on alkaline-earth atoms offer a particular high accuracy and improvement in comparison to classic sensors. Laboratory based experiments are rapidly transitioning to field applicable quantum sensors and have also seen a beginning commercialization. To facilitate this transition, a reduction of size, weight and power consumption in the form of miniaturization of key components such as the magneto-optical trap is necessary. In this work, I present design and characterization of two planar structures for cooling on a broad-line and a narrow-line transition at two different wavelengths with a single, incident bi-chromatic beam. The first is a two-color grating magneto-optical trap (GMOT) optimized for cooling and trapping of 88Sr atoms on the first and second cooling transition. Secondly, a quasi-planar, achromatic Fresnel structure for magneto-optical trapping combining the advantages of achromaticity of the tetrahedral MOT with robustness, small size and ample optical access of the GMOT is presented. In the GMOT, 106 88Sr atoms are initially cooled on the 1S0 ! 1P1 transition at 461nm to few mK and subsequently transferred to the second cooling stage on the narrow line 1S0 ! 3P1 transition at 689nm where they are further cooled to a temperature of < 5 K. A transfer efficiency of 25% is reached. I outline general design considerations for two-color cooling with a GMOT on a broad and narrow transition transferable to other atom species. In the so-called Fresnel MOT a comparable number of 88Sr were precooled on the 1S0 ! 1P1 transition and subsequently cooled on the 1S0 ! 3P1 transition with a transfer efficiency of 50%. Here, they were further cooled in the so-called broadband MOT to temperatures of 20 K-40 K. Fermionic strontium was also successfully captured in the first stage MOT. Due to its achromaticity, the Fresnel MOT can be used for laser cooling of any atom where materials with suitable reflectivity are available and can further be used for even multi-species traps. Furthermore, I analyze MOT dynamics in micro-gravity applications regarding their temperature and number density and consequences for trap design for space-borne applications. These results enable compact, robust set-ups for multi-color MOTs paving the way for largely miniaturized physics packages in quantum sensing.

QUEST-Leibniz Research School
Doctoral thesis
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