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arXiv:2502.17310 · Physical Review A

Hyperfine and Zeeman optical pumping and transverse laser cooling of a thermal atomic beam of dysprosium using a single 421-nm laser

Rohan Chakravarthy, Jonathan Agil, Arijit Sharma, Jung Bog Kim, Dmitry Budker

Published Feb 3, 2026• 1 citation
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Abstract

We demonstrate the effect of Zeeman and hyperfine optical pumping and transverse laser cooling of a dysprosium (Dy) atomic beam on the 4 f 10 6 s 2 ( J = 8 ) → 4 f 10 6 s 6 p ( J = 9 ) transition at 421.291 nm. For Dy 163 , a custom-built electro-optic modulator is used to generate five frequency sidebands required to pump the atoms to the F = 10.5 ground-state hyperfine level, and the light polarization is chosen to pump the atoms to the m F = 10.5 Zeeman sublevel. The atoms are simultaneously laser cooled using a standing wave orthogonal to the atomic beam. The resulting polarized and cooled atomic beam will be used in fundamental physics experiments taking advantage of the “accidental” degeneracy of excited states in Dy, including the ongoing measurement of parity violation in this system.

DOI
10.1103/vnsn-pyd1

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•Jan 24, 2025•0 citations
We demonstrate the effect of Zeeman and hyperfine optical pumping and transverse laser cooling of a dysprosium (Dy) atomic beam on the 4 f 10 6 s 2 ( J = 8 ) → 4 f 10 6 s 6 p ( J = 9 ) transition at 421.291 nm. For Dy 163 , a custom-built electro-optic modulator is used to generate five frequency sidebands required to pump the atoms to the F = 10.5 ground-state hyperfine level, and the light polarization is chosen to pump the atoms to the m F = 10.5 Zeeman sublevel. The atoms are simultaneously laser cooled using a standing wave orthogonal to the atomic beam. The resulting polarized and cooled atomic beam will be used in fundamental physics experiments taking advantage of the “accidental” degeneracy of excited states in Dy, including the ongoing measurement of parity violation in this system.
A thermal atomic beam of dysprosium atoms is cooled using the $4{f}^{10}6{s}^{2}(J=8)\ensuremath{\rightarrow}4{f}^{10}6s6p(J=9)$ transition at 421421421 nm. The cooling is done via a standing light wave orthogonal to the atomic beam. Efficient transverse cooling to the Doppler limit is demonstrated for all observable isotopes of dysprosium. Branching ratios to metastable states are demonstrated to be <<<$5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. A scheme for enhancement of the nonzero-nuclear-spin-isotope cooling and a method for direct identification of possible trap states are proposed.
The laser cooling and trapping of ultracold neutral dysprosium has been demonstrated recently using the broad, open, 421-nm cycling transition. Narrow-line magneto-optical trapping of Dy on longer wavelength transitions would enable the preparation of ultracold Dy samples suitable for loading optical dipole traps and subsequent evaporative cooling. We have identified the closed 741-nm cycling transition as a candidate for the narrow-line cooling of Dy. We present experimental data on the isotope shifts, the hyperfine constants AAA and BBB, and the decay rate of the 741-nm transition. In addition, we report a measurement of the 421-nm transition's linewidth, which agrees with previous measurements. We summarize the laser-cooling characteristics of these transitions as well as other narrow cycling transitions that may prove useful for cooling Dy.
We present measurements of the hyperfine coefficients and isotope shifts of the Dy I 683.731 nm transition, using saturated absorption spectroscopy on an atomic beam. A King Plot is drawn resulting in an updated value for the specific mass shift δν(684,sms)(164-162)=-534±17 MHz. Using fluorescence spectroscopy, we measure the excited state lifetime τ684=1.68(5) μs, yielding a linewidth of γ684=95±3 kHz. We give an upper limit to the branching ratio between the two decay channels from the excited state showing that this transition is usable for optical pumping into a dark state and demagnetization cooling.
We use two-laser optical pumping on a continuous atomic fountain in order to prepare cold cesium atoms in the same quantum ground state. A first laser excites the F=4F=4F=4 ground state to pump the atoms toward F=3F=3F=3 while a second $\ensuremath{\pi}$-polarized laser excites the $F=3\ensuremath{\rightarrow}{F}^{'}=3$ transition of the D2{D}_{2}D2​ line to produce Zeeman pumping toward m=0m=0m=0. To avoid trap states, we implement the first laser in a two-dimensional optical lattice geometry, thereby creating polarization gradients. This configuration has the advantage of simultaneously producing Sisyphus cooling when the optical lattice laser is tuned between the $F=4\ensuremath{\rightarrow}{F}^{'}=4$ and $F=4\ensuremath{\rightarrow}{F}^{'}=5$ transitions of the D2{D}_{2}D2​ line, which is important to remove the heat produced by optical pumping. Detuning the frequency of the second $\ensuremath{\pi}$-polarized laser reveals the action of a mechanism improving both laser cooling and state-preparation efficiency. A physical interpretation of this mechanism is discussed.
Dysprosium is the most magnetic element on the periodic table, which gives it the potential to display exotic physics. To study magnetic interacting atoms, we plan to capture single atoms of Dysprosium in optical tweezers, as done with Rubidium atoms in [1]. The first step is a 3D magneto-optical trap (MOT), which combines the optical molasses technique [2] and spatial-dependent Zeeman splitting [3] to trap a cloud of Dysprosium atoms. The MOT is inside an ultra-high vacuum (UHV) chamber and an effusion cell produces a hot beam of Dysprosium atoms, from which it loads. An amplified external cavity diode laser, locked to an optical reference cavity, generates the 421 nm light that forms the optical molasses. Water-cooled coils in a quadrupole configuration generate the magnetic fields. Our experiment is the first to load the MOT directly in the hot beam, prioritising simplicity over a large MOT population by going without a 2D MOT or Zeeman slower, used in [4] and [5]. This thesis presents our design and implementation of the simple Dysprosium MOT, shown in Fig. 1. We also show the characteristics of the MOT and atomic source. The simplification of the Dysprosium MOT is twofold: it does not require frequency doubling setups to generate the laser light [5,6] and the aforementioned pre-cooling stages [5,7]. Simplifying this process allows more laboratories worldwide to implement Dysprosium trapping and further our understanding of its exotic physics.