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arXiv:2509.04635 · Physical Review A

Simulated laser cooling and magneto-optical trapping of group-IV atoms

Geoffrey Zheng, Jianwei Wang, Mohit Verma, Qian Wang, Thomas Langin, David P. DeMille

Published Feb 20, 2026• 1 citation
arXivHTMLPDF

Abstract

We present a scheme for laser cooling and magneto-optical trapping of the Group IV (a.k.a. Group 14 or tetrel) atoms silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). These elements each possess a strong Type-II transition ($J \rightarrow J' = J-1$) between the metastable $s^2p^2 \,^3P_1$ state and the excited $s^2ps'\, ^3P_0^o$ state at an accessible laser wavelength, making them amenable to laser cooling and trapping. We focus on the application of this scheme to Sn, which has several features that make it attractive for precision measurement applications. We perform numerical simulations of atomic beam slowing, capture into a magneto-optical trap (MOT), and subsequent sub-Doppler cooling and compression in a blue-detuned MOT of Sn atoms. We also discuss a realistic experimental setup for realizing a high phase-space density sample of Sn atoms.

DOI
10.1103/3g5j-f935

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We present a scheme for laser cooling and magneto-optical trapping of the Group IV (a.k.a. Group 14 or tetrel) atoms silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). These elements each possess a strong Type-II transition (J→J′=J−1J \rightarrow J' = J-1J→J′=J−1) between the metastable s2p2 3P1s^2p^2 \,^3P_1s2p23P1​ state and the excited s2ps′ 3P0os^2ps'\, ^3P_0^os2ps′3P0o​ state at an accessible laser wavelength, making them amenable to laser cooling and trapping. We focus on the application of this scheme to Sn, which has several features that make it attractive for precision measurement applications. We perform numerical simulations of atomic beam slowing, capture into a magneto-optical trap (MOT), and subsequent sub-Doppler cooling and compression in a blue-detuned MOT of Sn atoms. We also discuss a realistic experimental setup for realizing a high phase-space density sample of Sn atoms.
Laser cooling and trapping of the heavy alkaline-earth-metal element barium has been achieved based on the strong $6{s}^{2}\text{ }{^{1}S}_{0}\text{\ensuremath{-}}6s6p\text{ }{^{1}P}_{1}$ transition. The excited state decays to a large fraction into metastable DDD states. Two schemes were implemented where three additional laser-driven transitions provide closed cooling cycles. This results in a fraction of 50(20)% of the trapped atoms in one of the metastable states. A total efficiency of $0.4(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ for slowing a thermal atomic beam and capturing atoms into a magneto-optical trap was obtained. Trap lifetimes of more than 1.5 s were observed. They are shortened at high laser intensities by three photon photoionization losses. The developed scheme can be transferred to other systems with large leakage from the cooling transition, such as Ra which is interesting for sensitive fundamental symmetry research.
We demonstrate sub-Doppler laser cooling and magneto-optical trapping of the rare earth element Holmium. Atoms are loaded from an atomic beam source and captured in six-beam σ+−σ−σ_+ - σ_-σ+​−σ−​ molasses using a strong J=15/2↔J=17/2J=15/2 \leftrightarrow J=17/2J=15/2↔J=17/2 cycling transition at λ=410.5nmλ=410.5 \rm nmλ=410.5nm. Due to the small difference in hyperfine splittings and Landé ggg-factors in the lower and upper levels of the cooling transition the MOT is self-repumped without additional repump light, and deep sub-Doppler cooling is achieved with the magnetic trap turned on. We measure the leakage out of the cycling transition to metastable states and find a branching ratio ∼10−5\sim 10^{-5}∼10−5 which is adequate for state resolved measurements on hyperfine encoded qubits.
We realize a magneto-optical trap (MOT) of titanium (Ti) atoms, performing laser cooling on the 498 nm transition between the long-lived 3 d 3 ( F 4 ) 4 s a 5 F 5 metastable state and the 3 d 3 ( F 4 ) 4 p y 5 G 6 o excited state. Without the addition of any repumping light, we observe MOTs of the three stable, I = 0 bosonic isotopes, Ti 46 , Ti 48 , and Ti 50 . Up to 8.30 ( 26 ) × 10 5 Ti 48 atoms are trapped at a maximum density of 1.3 ( 4 ) × 10 11 cm − 3 and at a temperature of 90 ( 15 ) µ K . By measuring the decay of the MOT, we constrain the leakage branching ratio of the cooling transition ( ≤ 2.5 × 10 − 6 ) and the two-body loss coefficient ( ≤ 2 × 10 − 10 cm 3 s − 1 ). Our approach to laser cooling Ti can be applied to other transition metals, enabling a significant expansion of the elements that can be laser cooled.
Laser cooling and trapping of heavy alkaline-earth element barium have been demonstrated for the first time ever. For any possible cycling transition in barium that could provide strong cooling forces, the excited state has a very large branching probability to metastable states. Additional lasers are thus needed to bring the atoms back in to the cooling cycle. In this work barium atoms were efficiently collected in a magneto-optical trap (MOT) by large optical forces from the strong 6s2 1S0 – 6s6p 1P1 transition. Trapping of barium has been achieved using up to seven lasers simultaneously. The properties of the barium MOT were characterized. The efficiency of capturing an atom from a thermal atomic beam into the MOT is 0.4(1) %. The developed scheme is very efficient for collecting atoms. Loss rate mechanisms from the trap were studied by observing the decay of the trap population. Typical lifetimes of the MOT cloud are on the order of one second and are limited mainly due to insufficient repumping of metastable states. The range of velocities from which barium atoms can be captured into the MOT is about 30 m/s. Different laser transitions were employed for repumping barium atoms from the 6s5d 3D1 and the 6s5d 3D2 states. They lead to similar trap populations and lifetimes. The temperature of the cold atomic barium cloud was determined to about 5 mK. Atomic properties of the 5d2 3F2 state were studied with trapped atoms, in particular it's lifetime was determined as 160(10) s. This work has shown a possible scheme to trap atoms with a leaky cooling cycle. Since atoms with such properties are the majority of the elements in the periodic table, the number of optically trapable elements can be significantly enlarged. Of particular high interest is radium, which is chemical homologue to barium. The interest in radium stems from it's high sensitivity to possible nuclear and electron permanent electric dipole moments (EDM's). An EDM violates parity as well as time reversal and is therefore of fundamental importance. Searches for such EDM's are among the main research goals of the recently commissioned TRImP facility at KVI.
Laser cooling on weak transitions is a useful technique for reaching ultracold temperatures in atoms with multiple valence electrons. However, for strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT) is destabilized by competition between optical and magnetic forces. We overcome this difficulty in Er by developing an unusual narrow-line MOT that balances optical and magnetic forces using laser light tuned to the blue side of a narrow (8 kHz) transition. The trap population is spin polarized with temperatures reaching below 2 muK. Our results constitute an alternative method for laser cooling on weak transitions, applicable to rare-earth-metal and metastable alkaline earth elements.
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