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

arXiv:2309.16835 · Physical Review A

Hyperfine structure of the A1Π state of AlCl and its relevance to laser cooling and trapping

John R. Daniel, Jamie Shaw, Chen Wang, Liren Liu, Brian K. Kendrick, Boerge Hemmerling, Daniel McCarron

Published Dec 26, 2023• 6 citations
arXivHTMLPDF

Abstract

The majority of molecules proposed for laser cooling and trapping experiments have $\mathrm{\ensuremath{\Sigma}}$-type ground states. Specifically, ${}^{2}\mathrm{\ensuremath{\Sigma}}$ states have cycling transitions analogous to ${D}_{1}$ lines in alkali-metal atoms while ${}^{1}\mathrm{\ensuremath{\Sigma}}$ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with ${}^{2}\mathrm{\ensuremath{\Sigma}}$-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed ${}^{1}\mathrm{\ensuremath{\Sigma}}$-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl---a ${}^{1}\mathrm{\ensuremath{\Sigma}}$ molecule---and report on the characterization of the ${A}^{1}\mathrm{\ensuremath{\Pi}}$ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using ab initio calculations, we identify the photodissociation via a ${3}^{1}\mathrm{\ensuremath{\Pi}}$ state and photoionization process via the ${3}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state as possible loss mechanisms for a magneto-optical trap of AlCl.

DOI
10.1103/physreva.108.062821

Related papers

Magneto-Optical Trapping of Aluminum Monofluoride

E. Padilla, J. Cai, P. Agarwal +6 more

Magneto-optical trapping of molecules has thus far been restricted to molecules with 2Σ electronic ground states. These species are chemically reactive and only support a simple laser cooling scheme from their first excited rotational level. Here, we demonstrate a magneto-optical trap (MOT) of aluminum monofluoride (AlF), a deeply bound and intrinsically stable diatomic molecule with a 1Σ+ electronic ground state. The MOT operates on the strong A1ΠX1ΠΣ+ transition near 227.5 nm, whose Q(J) lines are all rotationally closed. We demonstrate a MOT of about 64 molecules for the J = 1 level of AlF, more than 104 molecules for J = 2 and 3, and with no fundamental limit in going to higher rotational levels. Laser cooling and trapping of AlF is conceptually similar to the introduction of alkaline-earth atoms into cold atom physics, and is key to leveraging its spin-forbidden a3ΠX1Σ+ transition for precision spectroscopy and narrow-line cooling.

•Dec 12, 2025•0 citations

Magneto-Optical Trapping of Aluminum Monofluoride

J. E. Padilla‐Castillo, J. Cai, P. Agarwal +6 more

Magneto-optical trapping of molecules has thus far been restricted to molecules with ^{2}Σ electronic ground states. These species are chemically reactive and only support a simple laser cooling scheme from their first excited rotational level. Here, we demonstrate a magneto-optical trap (MOT) of aluminum monofluoride (AlF), a deeply bound and intrinsically stable diatomic molecule with a ^{1}Σ^{+} electronic ground state. The MOT operates on the strong A^{1}Π←X^{1}Σ^{+} transition near 227.5 nm, whose Q(J) lines are all rotationally closed. We demonstrate a MOT of about 6×10^{4} molecules for the J=1 level of AlF, more than 10^{4} molecules for J=2 and 3, and with no fundamental limit in going to higher rotational levels. Laser cooling and trapping of AlF is conceptually similar to the introduction of alkaline-earth atoms into cold atom physics, and is key to leveraging its spin-forbidden a^{3}Π←X^{1}Σ^{+} transition for precision spectroscopy and narrow-line cooling.

arXiv:2506.02266•Physical Review Letters•Oct 17, 2025•10 citations

Magneto-optical trapping of barium

Subhadeep De, Umakanth Dammalapati, Klaus Peter Jungmann +1 more

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 $D$ 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.

arXiv:0807.4100•Physical Review A•Apr 13, 2009•73 citations

Theoretical Investigation of Spectroscopic Properties of the Alkaline-Earth-Metal Monohydrides toward Laser Cooling and Magneto-Optical Trapping

Renjun Pang, J. H. Yin, Yueyang Wang +7 more

High Resolution Image Download MS PowerPoint Slide Alkaline-earth-metal monohydrides M H ( M = Be, Mg, Ca, Sr, Ba) have long been regarded as promising candidates toward laser cooling and trapping; however, their rich internal level structures that are amenable to magneto-optical trapping have not been completely explored. Here, we first systematically evaluated Franck–Condon factors of these alkaline-earth-metal monohydrides in the A 2 Π 1/2 ← X 2 Σ + transition, exploiting three respective methods (the Morse potential, the closed-form approximation, and the Rydberg–Klein–Rees method). The effective Hamiltonian matrix was introduced for MgH, CaH, SrH, and BaH individually in order to figure out their molecular hyperfine structures of X 2 Σ +, the transition wavelengths in the vacuum, and hyperfine branching ratios of A 2 Π 1/2 ( J ′ = 1/2,+) ← X 2 Σ + ( N = 1,−), followed by possible sideband modulation proposals to address all hyperfine manifolds. Lastly, the Zeeman energy level structures and associated magnetic g factors of the ground state X 2 Σ + ( N = 1,−) were also presented. Our theoretical results here not only shed more light on the molecular spectroscopy of alkaline-earth-metal monohydrides toward laser cooling and magneto-optical trapping but also can contribute to research in molecular collisions involving few-atom molecular systems, spectral analysis in astrophysics and astrochemistry, and even precision measurement of fundamental constants such as the quest for nonzero detection of electron’s electric dipole moment.

ACS Omega•May 24, 2023•5 citations

SPECTROSCOPY ON ALUMINUM MONOCHLORIDE (ALCL) FOR LASER COOLING AND TRAPPING

Boerge Hemmerling, Shan-Wen Tsai, Christopher J. Bardeen +7 more

Cooling atoms to the ultracold regime has allowed for studies of physics, ranging from many-body physics of quantum degenerate gases, quantum computing, precision measurements and tests of fundamental symmetries. Extending these experiments to polar molecules has the prospect of enhancing the sensitivity of such tests and of enabling novel studies, such as cold controlled chemistry. However, applying traditional laser cooling techniques to molecules is rendered difficult due their additional degrees of freedom which result in a limited photon scattering budget. Here we study aluminum monochloride (AlCl) as a promising candidate for laser cooling and trapping. The cooling transition at 261 nm ($A^{1} \Pi - X^{1} \Sigma^{+}$) has a theoretical Franck-Condon factor of 99.88\% which allows for scattering ~800 photons with a single laser before the molecule enters an excited vibrational state. We use a frequency-tripled (SHG + SFG) Titanium-Sapphire laser and generate AlCl via laser ablation in a cryogenic helium buffer gas beam source. We will present our spectroscopy results on AlCl and the measured molecular constants of the $A^{1}\Pi$ state and compare them with ab-initio calculations. We will also discuss our estimates on the Franck-Condon factors.

International Symposium on Molecular Spectroscopy (ISMS)•Jun 24, 2021•1 citation

Vibrational branching ratios and hyperfine structure of 11BH and its suitability for laser cooling

Richard Hendricks, Darren Holland, Stefan Truppe +2 more

The simple structure of the BH molecule makes it an excellent candidate for direct laser cooling. We measure the branching ratios for the decay of the A^{1}Pi (v'=0) state to vibrational levels of the ground state, X^{1}Sigma^{+}, and find that they are exceedingly favourable for laser cooling. We verify that the branching ratio for the spin-forbidden transition to the intermediate a^{3}Pi state is inconsequentially small. We measure the frequency of the lowest rotational transition of the X state, and the hyperfine structure in the relevant levels of both the X and A states, and determine the nuclear electric quadrupole and magnetic dipole coupling constants. Our results show that, with a relatively simple laser cooling scheme, a Zeeman slower and magneto-optical trap can be used to cool, slow and trap BH molecules.

arXiv:1404.6174•Frontiers in Physics•Aug 19, 2014•33 citations
The majority of molecules proposed for laser cooling and trapping experiments have \ensuremathΣ\mathrm{\ensuremath{\Sigma}}\ensuremathΣ-type ground states. Specifically, 2\ensuremathΣ{}^{2}\mathrm{\ensuremath{\Sigma}}2\ensuremathΣ states have cycling transitions analogous to D1{D}_{1}D1​ lines in alkali-metal atoms while 1\ensuremathΣ{}^{1}\mathrm{\ensuremath{\Sigma}}1\ensuremathΣ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with 2\ensuremathΣ{}^{2}\mathrm{\ensuremath{\Sigma}}2\ensuremathΣ-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed 1\ensuremathΣ{}^{1}\mathrm{\ensuremath{\Sigma}}1\ensuremathΣ-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl---a 1\ensuremathΣ{}^{1}\mathrm{\ensuremath{\Sigma}}1\ensuremathΣ molecule---and report on the characterization of the A1\ensuremathΠ{A}^{1}\mathrm{\ensuremath{\Pi}}A1\ensuremathΠ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using ab initio calculations, we identify the photodissociation via a 31\ensuremathΠ{3}^{1}\mathrm{\ensuremath{\Pi}}31\ensuremathΠ state and photoionization process via the 31\ensuremathΣ+{3}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}31\ensuremathΣ+ state as possible loss mechanisms for a magneto-optical trap of AlCl.
Magneto-optical trapping of molecules has thus far been restricted to molecules with 2Σ electronic ground states. These species are chemically reactive and only support a simple laser cooling scheme from their first excited rotational level. Here, we demonstrate a magneto-optical trap (MOT) of aluminum monofluoride (AlF), a deeply bound and intrinsically stable diatomic molecule with a 1Σ+ electronic ground state. The MOT operates on the strong A1ΠX1ΠΣ+ transition near 227.5 nm, whose Q(J) lines are all rotationally closed. We demonstrate a MOT of about 64 molecules for the J = 1 level of AlF, more than 104 molecules for J = 2 and 3, and with no fundamental limit in going to higher rotational levels. Laser cooling and trapping of AlF is conceptually similar to the introduction of alkaline-earth atoms into cold atom physics, and is key to leveraging its spin-forbidden a3ΠX1Σ+ transition for precision spectroscopy and narrow-line cooling.
Magneto-optical trapping of molecules has thus far been restricted to molecules with ^{2}Σ electronic ground states. These species are chemically reactive and only support a simple laser cooling scheme from their first excited rotational level. Here, we demonstrate a magneto-optical trap (MOT) of aluminum monofluoride (AlF), a deeply bound and intrinsically stable diatomic molecule with a ^{1}Σ^{+} electronic ground state. The MOT operates on the strong A^{1}Π←X^{1}Σ^{+} transition near 227.5 nm, whose Q(J) lines are all rotationally closed. We demonstrate a MOT of about 6×10^{4} molecules for the J=1 level of AlF, more than 10^{4} molecules for J=2 and 3, and with no fundamental limit in going to higher rotational levels. Laser cooling and trapping of AlF is conceptually similar to the introduction of alkaline-earth atoms into cold atom physics, and is key to leveraging its spin-forbidden a^{3}Π←X^{1}Σ^{+} transition for precision spectroscopy and narrow-line cooling.
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.
High Resolution Image Download MS PowerPoint Slide Alkaline-earth-metal monohydrides M H ( M = Be, Mg, Ca, Sr, Ba) have long been regarded as promising candidates toward laser cooling and trapping; however, their rich internal level structures that are amenable to magneto-optical trapping have not been completely explored. Here, we first systematically evaluated Franck–Condon factors of these alkaline-earth-metal monohydrides in the A 2 Π 1/2 ← X 2 Σ + transition, exploiting three respective methods (the Morse potential, the closed-form approximation, and the Rydberg–Klein–Rees method). The effective Hamiltonian matrix was introduced for MgH, CaH, SrH, and BaH individually in order to figure out their molecular hyperfine structures of X 2 Σ +, the transition wavelengths in the vacuum, and hyperfine branching ratios of A 2 Π 1/2 ( J ′ = 1/2,+) ← X 2 Σ + ( N = 1,−), followed by possible sideband modulation proposals to address all hyperfine manifolds. Lastly, the Zeeman energy level structures and associated magnetic g factors of the ground state X 2 Σ + ( N = 1,−) were also presented. Our theoretical results here not only shed more light on the molecular spectroscopy of alkaline-earth-metal monohydrides toward laser cooling and magneto-optical trapping but also can contribute to research in molecular collisions involving few-atom molecular systems, spectral analysis in astrophysics and astrochemistry, and even precision measurement of fundamental constants such as the quest for nonzero detection of electron’s electric dipole moment.
Cooling atoms to the ultracold regime has allowed for studies of physics, ranging from many-body physics of quantum degenerate gases, quantum computing, precision measurements and tests of fundamental symmetries. Extending these experiments to polar molecules has the prospect of enhancing the sensitivity of such tests and of enabling novel studies, such as cold controlled chemistry. However, applying traditional laser cooling techniques to molecules is rendered difficult due their additional degrees of freedom which result in a limited photon scattering budget. Here we study aluminum monochloride (AlCl) as a promising candidate for laser cooling and trapping. The cooling transition at 261 nm (A1Π−X1Σ+A^{1} \Pi - X^{1} \Sigma^{+}A1Π−X1Σ+) has a theoretical Franck-Condon factor of 99.88\% which allows for scattering ~800 photons with a single laser before the molecule enters an excited vibrational state. We use a frequency-tripled (SHG + SFG) Titanium-Sapphire laser and generate AlCl via laser ablation in a cryogenic helium buffer gas beam source. We will present our spectroscopy results on AlCl and the measured molecular constants of the A1ΠA^{1}\PiA1Π state and compare them with ab-initio calculations. We will also discuss our estimates on the Franck-Condon factors.
The simple structure of the BH molecule makes it an excellent candidate for direct laser cooling. We measure the branching ratios for the decay of the A^{1}Pi (v'=0) state to vibrational levels of the ground state, X^{1}Sigma^{+}, and find that they are exceedingly favourable for laser cooling. We verify that the branching ratio for the spin-forbidden transition to the intermediate a^{3}Pi state is inconsequentially small. We measure the frequency of the lowest rotational transition of the X state, and the hyperfine structure in the relevant levels of both the X and A states, and determine the nuclear electric quadrupole and magnetic dipole coupling constants. Our results show that, with a relatively simple laser cooling scheme, a Zeeman slower and magneto-optical trap can be used to cool, slow and trap BH molecules.