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Bulletin of the American Physical Society

Towards an AC-MOT of CaF

Loïc Anderegg, Eunmi Chae, Aakash Ravi, Benjamin L. Augenbraun, Boerge Hemmerling, Garrett K. Drayna, Nicholas R. Hutzler, Alejandra Collopy, Yewei Wu, Shiqian Ding, Jun Ye, Wolfgang Ketterle, John M. Doyle

Published May 24, 2016• 0 citations
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Progress towards a MOT for CaF

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Bulletin of the American Physical Society•Jun 5, 2012•1 citation

Laser Slowing of CaF Molecules and Progress Towards a Dual-MOT for Li and CaF

Eunmi Chae

Diatomic molecules are considered good candidates for the study of strongly correlated systems and precision measurement searches due to their combination of complex internal states and strong long-range interactions. Cooling molecules down to ultracold temperatures is often a necessary step for fully utilizing the power of the molecule. This requires a trap for molecules and the ability to cool molecules to the mK regime and below. A magneto-optical trap (MOT) is a good tool for achieving mK temperatures. However, extra care is needed for molecules to form the necessary quasi-closed cycling transitions due to molecule's complicated energy structure. In our work with CaF, we use two repump lasers to block vibrational leakage and selection rules for the rotational degree of freedom to achieve about 10^{5} photon cycles.\n\n\n\nThe two-stage buffer gas beam source is a general method to generate a cold and slow beam of molecules with a forward velocity of about 50 m/s. The compatibility of the buffer-gas source with a MOT is studied and we confirm that such beams can be nicely compatible with MOTs using various atomic species. \n\n\n\nIn order to load molecules into a MOT from even such a slow beam, additional slowing is required due to the low capture velocity of a molecular MOT (< 10 m/s). We apply a frequency-broadened “white-light” slowing on CaF from a two-stage source, demonstrating slowing of CaF below 10 m/s. An AC MOT, which provides active remixing of dark substates, is also developed and Li atoms are slowed and trapped. These are crucial ingredients for co-trapping CaF molecules and Li atoms and study their collisional properties, which would lead to sympathetic cooling of molecules down to ultracold temperatures. \n\n\n\nThe achievement of slowing and development of this system allowed for the detailed study of the CaF laser cooling system, as well as physical processes involved with AC MOTs and the proposed MOT for CaF. Crucial knowledge of this archetypal system provides significant progress toward manipulation and control of molecules similar to what has been achieved with atoms and what is necessary for searches for new physics with ultracold molecules.

•Jan 27, 2016•1 citation

Blue-detuned molecular magneto-optical trap schemes based on Bayesian optimization

S. Xu, R. X. Li, Yong Xia +2 more

Direct laser cooling and trapping of molecules to temperature below the Doppler limit and density exceeding ${10}^{8}$ 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.

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One-dimensional magneto-optical compression of a cold CaF molecular beam

Eunmi Chae, Loïc Anderegg, Benjamin L. Augenbraun +7 more

We demonstrate the one-dimensional, transverse magneto-optical compression of a cold beam of calcium monofluoride (CaF). By continually alternating the magnetic field direction and laser polarizations of the magneto-optical trap (RF MOT), a photon scattering rate of is achieved. A 3D model for this RF MOT, validated by agreement with data, predicts a 3D RF MOT capture velocity for CaF of 5 m s –1 .

arXiv:1701.03254•New Journal of Physics•Mar 3, 2017•17 citations

Further Developments and Applications

Lecture notes in physics. M, Monographs•Sep 10, 2008•0 citations
Diatomic molecules are considered good candidates for the study of strongly correlated systems and precision measurement searches due to their combination of complex internal states and strong long-range interactions. Cooling molecules down to ultracold temperatures is often a necessary step for fully utilizing the power of the molecule. This requires a trap for molecules and the ability to cool molecules to the mK regime and below. A magneto-optical trap (MOT) is a good tool for achieving mK temperatures. However, extra care is needed for molecules to form the necessary quasi-closed cycling transitions due to molecule's complicated energy structure. In our work with CaF, we use two repump lasers to block vibrational leakage and selection rules for the rotational degree of freedom to achieve about 10^{5} photon cycles.\n\n\n\nThe two-stage buffer gas beam source is a general method to generate a cold and slow beam of molecules with a forward velocity of about 50 m/s. The compatibility of the buffer-gas source with a MOT is studied and we confirm that such beams can be nicely compatible with MOTs using various atomic species. \n\n\n\nIn order to load molecules into a MOT from even such a slow beam, additional slowing is required due to the low capture velocity of a molecular MOT (< 10 m/s). We apply a frequency-broadened “white-light” slowing on CaF from a two-stage source, demonstrating slowing of CaF below 10 m/s. An AC MOT, which provides active remixing of dark substates, is also developed and Li atoms are slowed and trapped. These are crucial ingredients for co-trapping CaF molecules and Li atoms and study their collisional properties, which would lead to sympathetic cooling of molecules down to ultracold temperatures. \n\n\n\nThe achievement of slowing and development of this system allowed for the detailed study of the CaF laser cooling system, as well as physical processes involved with AC MOTs and the proposed MOT for CaF. Crucial knowledge of this archetypal system provides significant progress toward manipulation and control of molecules similar to what has been achieved with atoms and what is necessary for searches for new physics with ultracold molecules.
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.