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arXiv:2404.03636 · Physical Review Letters

High Compression Blue-Detuned Magneto-Optical Trap of Polyatomic Molecules

Christian Hallas, Grace K. Li, Nathaniel B. Vilas, Paige Robichaud, Loïc Anderegg, John M. Doyle

Published Dec 18, 2025• 11 citations
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Abstract

We demonstrate a blue-detuned magneto-optical trap (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). We identify a novel MOT frequency configuration that produces high spatial compression of the molecular cloud. This high compression MOT achieves a cloud radius of 59(5) μm and a peak density of 8(2)×10^{8} cm^{-3}. We experimentally compare several blue-detuned MOT schemes for CaOH and find good agreement between our data and Monte Carlo simulations.

DOI
10.1103/w9qc-rczf

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We demonstrate a blue-detuned magneto-optical trap (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). We identify a novel MOT frequency configuration that produces high spatial compression of the molecular cloud. This high compression MOT achieves a cloud radius of 59(5) μm and a peak density of 8(2)×10^{8} cm^{-3}. We experimentally compare several blue-detuned MOT schemes for CaOH and find good agreement between our data and Monte Carlo simulations.
We report magneto-optical trapping (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). The MOT contains 2.0(5)×1042.0(5)\times 10^42.0(5)×104 CaOH molecules at a peak density of 3.0(8)×1063.0(8)\times10^{6}3.0(8)×106 cm−3^{-3}−3. CaOH molecules are further sub-Doppler laser cooled in an optical molasses, to a temperature of 110(4) μμμK. The temperatures and densities achieved here make CaOH a viable candidate for a wide variety of quantum science applications, including the creation of optical tweezer arrays of CaOH molecules. This work also suggests that laser cooling and magneto-optical trapping of many other polyatomic species will be both feasible and practical.
We report the experimental realization of a conveyor-belt magneto-optical trap for calcium monofluoride (CaF) molecules. The obtained highly-compressed cloud has a mean radius of 64(5) μμμm and a peak number density of 3.6(5)×10103.6(5) \times 10^{10}3.6(5)×1010 cm−3^{-3}−3, a 600-fold increase over the conventional red-detuned MOTs of CaF, and the densest molecular MOT observed to date. Subsequent loading of these molecules into an optical dipole trap yields up to 2.6×1042.6 \times 10^42.6×104 trapped molecules at a temperature of 14(2) μμμK with a peak phase-space density of ∼2.4×10−6\sim 2.4 \times 10^{-6}∼2.4×10−6. This opens new possibilities for a range of applications utilizing high-density, optically trapped ultracold molecules.
Abstract Achieving high-density samples of laser-cooled molecules is a critical step toward advancing applications in precision measurements, ultracold chemistry and quantum science. We report the experimental realization of a high-density conveyor-belt magneto-optical trap for calcium monofluoride (CaF) molecules. The obtained highly-compressed cloud has a mean radius of 64(5) μ m and a peak number density of 3.6(5) x 10 10 cm -3 , a 600-fold increase over the conventional red-detuned MOTs of CaF, and the densest molecular MOT observed to date. Subsequent loading of these molecules into an optical dipole trap yields up to 2.6 x 10 4 trapped molecules at a temperature of 14(2) μ K with a peak phase-space density of ~2.4 x 10 -6 . This opens new possibilities for a range of applications utilizing high-density, optically trapped ultracold molecules.
We report optical trapping of a polyatomic molecule, calcium monohydroxide (CaOH). CaOH molecules from a magneto-optical trap are sub-Doppler laser cooled to $20(3)\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{K}$ in free space and loaded into an optical dipole trap. We attain an in-trap molecule number density of $3(1)\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ at a temperature of $57(8)\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{K}$. Trapped CaOH molecules are optically pumped into an excited vibrational bending mode, whose $\ensuremath{\ell}$-type parity doublet structure is a potential resource for a wide range of proposed quantum science applications with polyatomic molecules. We measure the spontaneous, radiative lifetime of this bending mode state to be $\ensuremath{\sim}0.7\text{ }\text{ }\mathrm{s}$.
Direct laser cooling and trapping of molecules to temperature below the Doppler limit and density exceeding 108{10}^{8}108 are challenging due to the sub-Doppler heating effects of a molecular magneto-optical trap (MOT). In our previous paper [S. Xu et al., Phys. Rev. Res. 4, L042036 (2022)], we presented a general approach to engineering the sub-Doppler force by tuning the AC Stark shift with the addition of a blue-detuned laser. Here, by employing the Bayesian optimization method to optical Bloch equations, we have identified multiple blue-detuned MOT schemes for the CaF molecule. From the three-dimensional Monte Carlo simulation, we obtained a MOT temperature and density of 14 $\textmu{}\mathrm{K}$ and $4.5\ifmmode\times\else\texttimes\fi{}{10}^{8} {\mathrm{cm}}^{\ensuremath{-}3}$, respectively. Our findings present a potential avenue for directly loading molecular MOTs into conservative traps, which can capitalize on the high density and low temperature of the MOTs.