Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Chinese Physics B

Collision of cold CaF molecules: Towards evaporative cooling

Y. T. Gu, Yunxia Huang, Chuanliang Li, Xiaohua Yang

Published Mar 1, 2019• 1 citation
Publisher

Abstract

Long range intermolecular interaction potential surface of CaF ( 2 Σ + ) was simulated by employing the MOLPRO program and using the RCCSD(T)/def2-TZVP theory. The predicted data were further fitted to obtain the collision cross-section. The elastic collision cross-section of CaF at the temperature around 2 mK is as high as 6.5×10 −9 cm 2 and the collision rate is over 4.1×10 6 Hz. Additionally, we found that an orientation electric field will simplify the intermolecular interaction potential function from quaternary into ternary and the collision cross-section will be raised by about three orders. All-optical evaporative cooling of cold CaF is discussed in the conclusion.

DOI
10.1088/1674-1056/28/3/033401

Related papers

Shielding collisions of ultracold CaF molecules with static electric fields

Bijit Mukherjee, Matthew D. Frye, C. Ruth Le Sueur +2 more

We study collisions of ultracold CaF molecules in strong static electric fields. These fields allow the creation of long-range barriers in the interaction potential, effectively preventing the molecules from reaching the short-range region where inelastic and other loss processes are likely to occur. We carry out coupled-channel calculations of rate coefficients for elastic scattering and loss. We develop an efficient procedure for including energetically well-separated rotor functions in the basis set via a Van Vleck transformation. We show that shielding is particularly efficient for CaF and allows the rate of two-body loss processes to be reduced by a factor of ${10}^{7}$ or more at a field of 23 kV/cm. The loss rates remain low over a substantial range of fields. Electron and nuclear spins cause strong additional loss in some small ranges of field, but have little effect elsewhere. These results pave the way for evaporative cooling of CaF towards quantum degeneracy.

arXiv:2305.07600•Physical Review Research•Aug 10, 2023•15 citations

Modeling sympathetic cooling of molecules by ultracold atoms

Jongseok Lim, Matthew D. Frye, Jeremy M. Hutson +1 more

We model sympathetic cooling of ground-state CaF molecules by ultracold Li and Rb atoms. The molecules are moving in a microwave trap, while the atoms are trapped magnetically. We calculate the differential elastic cross sections for CaF-Li and CaF-Rb collisions, using model Lennard-Jones potentials adjusted to give typical values for the $s$-wave scattering length. Together with trajectory calculations, these differential cross sections are used to simulate the cooling of the molecules, the heating of the atoms, and the loss of atoms from the trap. We show that a hard-sphere collision model based on an energy-dependent momentum transport cross section accurately predicts the molecule cooling rate but underestimates the rates of atom heating and loss. Our simulations suggest that Rb is a more effective coolant than Li for ground-state molecules, and that the cooling dynamics is less sensitive to the exact value of the $s$-wave scattering length when Rb is used. Using realistic experimental parameters, we find that molecules can be sympathetically cooled to $100\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ in about 10 s. By applying evaporative cooling to the atoms, the cooling rate can be increased and the final temperature of the molecules can be reduced to $1 \ensuremath{\mu}\mathrm{K}$ within 30 s.

arXiv:1508.03987•Physical Review A•Nov 13, 2015•55 citations

The He–CaH(2Σ+) interaction. II. Collisions at cold and ultracold temperatures

N. Balakrishnan, Gerrit C. Groenenboom, Roman V. Krems +1 more

We present cross sections for rotational, vibrational, and fine-structure transitions in He–CaH(2Σ) collisions at cold and ultracold temperatures calculated using the ab initio potential energy surface reported in the preceding paper. Rotational quenching is fast, vibrational quenching is slow. The spin-rotational interaction, although small and having no influence at temperatures above 10 K, changes significantly the rate coefficients for rotational quenching at lower temperatures. The theoretical rotational, vibrational, and elastic cross sections are compared with the results of a buffer gas cooling experiment carried out at a temperature of about 0.4 K. The theoretical predictions for the vibrational and elastic cross sections are larger than the measured values. The sensitivity to the potential energy surface is explored. A modified surface diminishes but does not remove the differences between theory and experiment.

The Journal of Chemical Physics•Apr 11, 2003•80 citations

Evaporative cooling of CaF in a magnetic-assisted electrostatic quadrupole shell-trap

Yuhang Shu, Xu-Ping Shao, Xiaohua Yang

Abstract A magnetic-assisted electric quadrupole trap (MAEQT) is proposed for trapping CaF molecules and enabling subsequent evaporative cooling, by leveraging the hybrid-field-induced perturbation effects. Our simulation demonstrates that experimentally available [Phys. Rev. Lett. 119, 103201, 2017] 1.10 × 10 5 CaF molecules, initially at a temperature of 340 μK, can be cooled down to 4.4 μK within the MAEQT. The trapped molecular cloud exhibits a shell-like configuration, with inner and outer diameters of 270 μm and 322 μm, respectively. Furthermore, the phase-space density is enhanced from 4.38 × 10 −9 to 4.09 × 10 −6 , representing a three-order-of-magnitude increase. This shell-shaped cold CaF ensemble might be employed for sympathetic cooling of various molecules–excluding bialkali species and those with highly diagonal Franck-Condon factors–to the tens of μK regime, which paves the way for their further quantum manipulation.

Physica Scripta•May 1, 2026•0 citations

Collisions between laser-cooled atoms and molecules

Sarunas Jurgilas

This thesis describes an experiment to produce the first laser cooled mixtures of atoms and polar molecules in magneto-optical and magnetic quadrupole traps. Inelastic collision processes between CaF molecules and Rb atoms are studied in both trapping arrangements. When molecules occupy the first rotationally excited state it is found that loss from either trap occurs at near the universal rate due to collisions with co-trapped atoms. When the molecular sample is transferred to the ground rotational state the loss rate is suppressed by at least an order of magnitude. The experimental results are compared to a quantum scattering model based on quantum defect theory and the results seem to be encouraging for observing a high ratio of elastic to inelastic collision rates in this system. In addition, improvements to the experimental apparatus are presented which led to the first measurements of the elastic cross-section for collisions between CaF and Rb. Although at the currently attainable number densities no thermalization is observed, an upper bound on the value of the cross section is placed.

Bulletin of the American Physical Society•Jul 1, 2021•0 citations

Cold collisions between boson or fermion molecules

Masatoshi Kajita

We theoretically investigate collisions between electrostatically trapped cold polar molecules and compare boson and fermion isotopes. Evaporative cooling seems possible for fermion molecules as the ratio of the collision loss cross section to the elastic collision cross section (R) gets smaller as the molecular temperature T lowers. With boson molecules, R gets larger as T lowers, which makes evaporative cooling difficult. The elastic collision cross section between fermion molecules can be larger than that for boson molecules with certain conditions.

Physical Review A•Jan 21, 2004•10 citations
Long range intermolecular interaction potential surface of CaF ( 2 Σ + ) was simulated by employing the MOLPRO program and using the RCCSD(T)/def2-TZVP theory. The predicted data were further fitted to obtain the collision cross-section. The elastic collision cross-section of CaF at the temperature around 2 mK is as high as 6.5×10 −9 cm 2 and the collision rate is over 4.1×10 6 Hz. Additionally, we found that an orientation electric field will simplify the intermolecular interaction potential function from quaternary into ternary and the collision cross-section will be raised by about three orders. All-optical evaporative cooling of cold CaF is discussed in the conclusion.
We study collisions of ultracold CaF molecules in strong static electric fields. These fields allow the creation of long-range barriers in the interaction potential, effectively preventing the molecules from reaching the short-range region where inelastic and other loss processes are likely to occur. We carry out coupled-channel calculations of rate coefficients for elastic scattering and loss. We develop an efficient procedure for including energetically well-separated rotor functions in the basis set via a Van Vleck transformation. We show that shielding is particularly efficient for CaF and allows the rate of two-body loss processes to be reduced by a factor of 107{10}^{7}107 or more at a field of 23 kV/cm. The loss rates remain low over a substantial range of fields. Electron and nuclear spins cause strong additional loss in some small ranges of field, but have little effect elsewhere. These results pave the way for evaporative cooling of CaF towards quantum degeneracy.
We model sympathetic cooling of ground-state CaF molecules by ultracold Li and Rb atoms. The molecules are moving in a microwave trap, while the atoms are trapped magnetically. We calculate the differential elastic cross sections for CaF-Li and CaF-Rb collisions, using model Lennard-Jones potentials adjusted to give typical values for the sss-wave scattering length. Together with trajectory calculations, these differential cross sections are used to simulate the cooling of the molecules, the heating of the atoms, and the loss of atoms from the trap. We show that a hard-sphere collision model based on an energy-dependent momentum transport cross section accurately predicts the molecule cooling rate but underestimates the rates of atom heating and loss. Our simulations suggest that Rb is a more effective coolant than Li for ground-state molecules, and that the cooling dynamics is less sensitive to the exact value of the sss-wave scattering length when Rb is used. Using realistic experimental parameters, we find that molecules can be sympathetically cooled to $100\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ in about 10 s. By applying evaporative cooling to the atoms, the cooling rate can be increased and the final temperature of the molecules can be reduced to $1 \ensuremath{\mu}\mathrm{K}$ within 30 s.
We present cross sections for rotational, vibrational, and fine-structure transitions in He–CaH(2Σ) collisions at cold and ultracold temperatures calculated using the ab initio potential energy surface reported in the preceding paper. Rotational quenching is fast, vibrational quenching is slow. The spin-rotational interaction, although small and having no influence at temperatures above 10 K, changes significantly the rate coefficients for rotational quenching at lower temperatures. The theoretical rotational, vibrational, and elastic cross sections are compared with the results of a buffer gas cooling experiment carried out at a temperature of about 0.4 K. The theoretical predictions for the vibrational and elastic cross sections are larger than the measured values. The sensitivity to the potential energy surface is explored. A modified surface diminishes but does not remove the differences between theory and experiment.
Abstract A magnetic-assisted electric quadrupole trap (MAEQT) is proposed for trapping CaF molecules and enabling subsequent evaporative cooling, by leveraging the hybrid-field-induced perturbation effects. Our simulation demonstrates that experimentally available [Phys. Rev. Lett. 119, 103201, 2017] 1.10 × 10 5 CaF molecules, initially at a temperature of 340 μK, can be cooled down to 4.4 μK within the MAEQT. The trapped molecular cloud exhibits a shell-like configuration, with inner and outer diameters of 270 μm and 322 μm, respectively. Furthermore, the phase-space density is enhanced from 4.38 × 10 −9 to 4.09 × 10 −6 , representing a three-order-of-magnitude increase. This shell-shaped cold CaF ensemble might be employed for sympathetic cooling of various molecules–excluding bialkali species and those with highly diagonal Franck-Condon factors–to the tens of μK regime, which paves the way for their further quantum manipulation.
This thesis describes an experiment to produce the first laser cooled mixtures of atoms and polar molecules in magneto-optical and magnetic quadrupole traps. Inelastic collision processes between CaF molecules and Rb atoms are studied in both trapping arrangements. When molecules occupy the first rotationally excited state it is found that loss from either trap occurs at near the universal rate due to collisions with co-trapped atoms. When the molecular sample is transferred to the ground rotational state the loss rate is suppressed by at least an order of magnitude. The experimental results are compared to a quantum scattering model based on quantum defect theory and the results seem to be encouraging for observing a high ratio of elastic to inelastic collision rates in this system. In addition, improvements to the experimental apparatus are presented which led to the first measurements of the elastic cross-section for collisions between CaF and Rb. Although at the currently attainable number densities no thermalization is observed, an upper bound on the value of the cross section is placed.
We theoretically investigate collisions between electrostatically trapped cold polar molecules and compare boson and fermion isotopes. Evaporative cooling seems possible for fermion molecules as the ratio of the collision loss cross section to the elastic collision cross section (R) gets smaller as the molecular temperature T lowers. With boson molecules, R gets larger as T lowers, which makes evaporative cooling difficult. The elastic collision cross section between fermion molecules can be larger than that for boson molecules with certain conditions.