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arXiv:2604.08876

Sub-Doppler laser cooling and optical transport of cesium with static magnetic fields

Tobias Bothwell, Junxin Chen, Brian M. Fields, Madeline Dawes, Anthony Reiter, Christina C. C. Willis, Jacob Scott, Michael McMaster, Farhad Majdeteimouri, Ilya Vinogradov, Seth Miers, Daniel C. Cole, Kevin M Loeffler, Ryan Jones, Marin Iliev, Jonathan Gilbert, Eric Copenhaver, Thomas Noël, A. G. Radnaev

Published Apr 10, 2026• 0 citations
arXivHTMLPDF

Abstract

Laser cooling of alkali atoms typically requires time-varying magnetic fields, introducing unwanted coupling between atom preparation and coherent operations. Here we demonstrate sub-Doppler laser cooling and optical transport of alkali atoms in a fully static magnetic-field configuration. Using a blue-detuned Type-II magneto-optical trap (MOT) operating on the closed $F=3 \rightarrow F'=2$ transition of the D2 line in cesium, we achieve temperatures of 17(1) $μ$K without changing the magnetic-field gradient between cooling stages. This enables direct loading into a shallow optical lattice and transport over 17 cm within the same static-field environment. In contrast to conventional alkali cooling schemes with dynamic fields, our approach establishes a continuous cooling and transport protocol compatible with static-field platforms. These results validate Type-II cooling as a practical technique for alkali atoms and provide a new route toward continuous-operation architectures in sensing and quantum computing.

DOI
10.48550/arxiv.2604.08876

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Laser cooling of alkali atoms typically requires time-varying magnetic fields, introducing unwanted coupling between atom preparation and coherent operations. Here we demonstrate sub-Doppler laser cooling and optical transport of alkali atoms in a fully static magnetic-field configuration. Using a blue-detuned Type-II magneto-optical trap (MOT) operating on the closed F=3→F′=2F=3 \rightarrow F'=2F=3→F′=2 transition of the D2 line in cesium, we achieve temperatures of 17(1) μμμK without changing the magnetic-field gradient between cooling stages. This enables direct loading into a shallow optical lattice and transport over 17 cm within the same static-field environment. In contrast to conventional alkali cooling schemes with dynamic fields, our approach establishes a continuous cooling and transport protocol compatible with static-field platforms. These results validate Type-II cooling as a practical technique for alkali atoms and provide a new route toward continuous-operation architectures in sensing and quantum computing.
Sub-Doppler cooling has been achieved for the two closed hyperfine transitions: F = 4 → F ' = 5 and F = 3 → F ' = 2, of the cesium D 2 line. One-dimension optical molasses is experimentally investigated and compared for both j → j + 1 and j → j - 1 transitions, on different laser polarization configurations, in the presence, and absence of a static magnetic field. One remarkable point is that cooling is obtained with blue laser detuning for the j → j - 1 transition. An applied static magnetic field can also shift the sub-Doppler-cooled molasses peaks to nonzero velocities without any extra heating, for the polarization gradient configurations.
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Sub-Doppler laser cooling of40K with Raman gray molasses on the D2{D}_{2}D2​ line
Gray molasses is a powerful tool for sub-Doppler laser cooling of atoms to low temperatures. For alkaline atoms, this technique is commonly implemented with cooling lasers which are blue-detuned from either the D 1 or D 2 line. Here we show that efficient gray molasses can be implemented on the D 2 line of 40 K with red -detuned lasers. We obtained temperatures of , which enables direct loading of atoms from a magneto-optical trap into an optical dipole trap. We support our findings by a one-dimensional model and three-dimensional numerical simulations of the optical Bloch equations which qualitatively reproduce the experimentally observed cooling effects.
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The main goal of this research is to cool potassium-41 atoms to ultracold temperatures (<10 μK) in order to study the spin dynamics of atom to atom interactions. However, our current goal is to finish constructing the apparatus that will allow us to confine and cool these atoms in three dimensions. This apparatus will cool and confine the potassium atoms in 3 steps. First, the atoms will be cooled and trapped in our 3D magneto-optical trap. This step of the experiment will cool the atoms near the Doppler-cooling limit, which for potassium atoms is 145 μK. Second, atoms will be loaded into a FORT (far off resonance trap) with an expected depth of 25 μK. In order to cool the atoms below the Doppler-cooling limit, we will use sub-Doppler cooling techniques. What is particularly unique about our experiment is that we plan to use an octupole magnetic field to achieve sub-Doppler cooling. In typical laser cooling experiments sub-Doppler temperatures are achieved when the quadrupole magnetic field is off, which leaves the atoms untrapped. Third, once the atoms have been loaded into the FORT one last cooling mechanism will be implemented. This mechanism is referred to as evaporative cooling and will cool the atoms below 10 μK.