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Chinese Physics B

Compact dual MOT apparatus of K and Rb for optical tweezer experiment

Kang Wei, Yangbo Wei, Shangjin Li, Bo Yan

Published Jun 26, 2025• 0 citations
Publisher

Abstract

Abstract The optical tweezer experiment with neutral atoms is widely used for quantum information research. Here, we present a compact dual magneto-optical trap (MOT) setup for a two-species optical tweezer. Rubidium (Rb) atoms are directly captured using a vapor MOT, while potassium (K) atoms are collected via a 2-stage MOT. Both the quadratic and gradient magnetic fields required for the MOT and Zeeman slower are created by permanent magnets. With the help of the Zeeman slower, the K MOT loading efficiency is enhanced by a factor of three. After the MOT stage, we apply D 1 gray molasses to reduce the temperature of the K atoms to 9 μK. Using this apparatus, both Rb and K are loaded into the optical tweezer.

DOI
10.1088/1674-1056/ade8e2

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Abstract The optical tweezer experiment with neutral atoms is widely used for quantum information research. Here, we present a compact dual magneto-optical trap (MOT) setup for a two-species optical tweezer. Rubidium (Rb) atoms are directly captured using a vapor MOT, while potassium (K) atoms are collected via a 2-stage MOT. Both the quadratic and gradient magnetic fields required for the MOT and Zeeman slower are created by permanent magnets. With the help of the Zeeman slower, the K MOT loading efficiency is enhanced by a factor of three. After the MOT stage, we apply D 1 gray molasses to reduce the temperature of the K atoms to 9 μK. Using this apparatus, both Rb and K are loaded into the optical tweezer.
We demonstrate a dual magneto-optical trap (MOT) of 109Ag^{109}\mathrm{Ag}109Ag and 39K^{39}\mathrm{K}39K. For silver, a decreasing-field Zeeman slower loads a MOT of $1.5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at a temperature of 0.74(5) mK, with laser cooling occurring primarily on the D2{D}_{2}D2​ line of $4{d}^{10}5s\phantom{\rule{0.28em}{0ex}}^{2}S_{1/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.28em}{0ex}}^{2}P_{3/2}$ at 328 nm. We create a Ag ``dark spot MOT,'' where shelving the atoms in a dark state enhances the captured atom number by a factor of 2 and the lifetime by a factor of 4. For potassium, we obtain $2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ trapped atoms, and further cooling on the D1{D}_{1}D1​ transition via gray molasses results in a cloud of $1.2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at $7(1)\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{K}$. We observe evidence of photoionization loss of the K MOT in the presence of Ag laser-cooling light, necessitating sequential rather than simultaneous loading for the two species. Our results on Ag point to simple and general laser cooling strategies for other coinage metals (Au, Cu). Furthermore, this work lays the foundation for the production of alkali-metal--coinage-metal degenerate quantum mixtures and highly polar molecules.
The optical tweezer experiment with neutral atoms is a focal topic in cold-atom physics due to its significant potential in quantum computing and simulation. Here we present the realization of a dual-species optical tweezer for both Rb and K atoms, taking a step towards creating a polar-molecule optical tweezer array. Initially, Rb and K atoms are collected using a dual magneto-optical trap and further cooled to $7\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{K}$ for Rb and $10\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{K}$ for K. By employing 850-nm tweezer beams, we demonstrate the ability to capture individual Rb or K atoms. The filling ratios of Rb and K can be finely adjusted by controlling the atomic densities of both species. Utilizing the postselection technique, we can create a deterministic array of two-species atoms, paving the way for future polar-molecule array formation.
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.
Abstract We outline an experimental setup for efficiently preparing a tweezer array of 88Sr atoms. Our setup uses permanent magnets to maintain a steady-state two-dimensional magneto-optical trap (MOT) which results in a loading rate of up to 108 s−1 at 5 mK for the three-dimensional blue MOT. This enables us to trap 2 × 106 88Sr atoms at 2 μK in a narrow-line red MOT with the 1S0 → 3P1 intercombination transition at 689 nm. With the Sisyphus cooling and pairwise loss processes, single atoms are trapped and imaged in 813 nm optical tweezers, exhibiting a lifetime of 2.5 min. We further investigate the survival fraction of a single atom in the tweezers and characterize the optical tweezer array using a release and recapture technique. Our experimental setup serves as an excellent reference for those engaged in experiments involving optical tweezer arrays, cold atom systems, and similar research.
We have built an apparatus for setting up a double magneto-optical trap (double MOT) which allows more than 10 Rb atoms to be loaded in 15 seconds. This compact system consists mainly of a stainless steel chamber and a homemade glass cell. The two chambers are spatially separated by a small diameter transfer tube for differential pumping. The stainless steel chamber is maintained at a pressure of 10 Torr, enabling fast capturing of background Rb atoms. The optically cooled atomic clouds are pushed by a laser beam towards the glass cell which is in a much higher vacuum. Under this condition, the glass cell provides a rather long life time for holding the atoms. After the atoms are loaded in the temporarily bright MOT, a semi-dark type MOT compression is employed to reach a spatial density of 1×10 atoms/cm. The compressed atom clouds are further cooled by polarization gradient cooling to a temperature of 30 μK. The high phase space density cloud is suitable for experiments related to ultracold atoms.
We present an experimental scheme for producing ultracold ytterbium atoms in a compact dual-chamber setup. A dispenser-loaded two-dimensional magneto-optical trap (MOT) using permanent magnets and operating on the broad ${}^{1}{S}_{0}\ensuremath{\rightarrow}{}^{1}{P}_{1}$ singlet transition delivers over 107{10}^{7}107 atoms per second through a differential pumping stage into a three-dimensional MOT. The two-color three-dimensional MOT uses the broad singlet transition to accumulate $\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{7}$ atoms of 174Yb{}^{174}\mathrm{Yb}174Yb within 2.5 s and subsequently the narrow ${}^{1}{S}_{0}\ensuremath{\rightarrow}{}^{3}{P}_{1}$ intercombination line to cool the atomic cloud to below 10 \textmu{}K. We report optimized parameters for each stage of the atom collection sequence, achieving high transfer efficiency. We find that shelving into the triplet state during the broad-transition MOT almost doubles the number of trapped atoms.