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

New Journal of Physics

Photodetachment and Doppler laser cooling of anionic molecules

S. Gerber, J. Fesel, M. Doser, D. Comparat

Published Jan 19, 2018• 23 citations
Publisher

Abstract

We propose to extend laser-cooling techniques, so far only achieved for neutral molecules, to molecular anions. A detailed computational study is performed for molecules stored in Penning traps using GPU based Monte Carlo simulations. Two cooling schemes—Doppler laser cooling and photodetachment cooling—are investigated. The sympathetic cooling of antiprotons is studied for the Doppler cooling scheme, where it is shown that cooling of antiprotons to subKelvin temperatures could becomes feasible, with impacts on the field of antimatter physics. The presented cooling schemes also have applications for the generation of cold, negatively charged particle sources and for the sympathetic cooling of other molecular anions.

DOI
10.1088/1367-2630/aaa951

Related papers

Laser Cooling of Molecular Anions

P. Yzombard, M. Hamamda, S. Gerber +2 more

We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_{2}^{-}, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped C_{2}^{-}, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.

arXiv:1506.06505•Physical Review Letters•May 27, 2015•93 citations

Optical dipole-force cooling of anions in a Penning trap

J. Fesel, S. Gerber, M. Doser +1 more

We discuss the possibility of using optical dipole forces for Sisyphus cooling of ions stored in a Penning trap by addressing the specific case of the molecular cooling candidate ${{\mathrm{C}}_{2}}^{\ensuremath{-}}$. Using a GPU accelerated code for Penning trap simulations, which we extended to include the molecule-light interaction, we show that this scheme can decrease the time required for cooling by an order of magnitude with respect to Doppler cooling. In our simulation we found that a reduction of the axial anion temperature from $10\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ to $50\phantom{\rule{0.28em}{0ex}}\mathrm{mK}$ in around $10\phantom{\rule{0.28em}{0ex}}\mathrm{s}$ is possible. The temperature of the radial degrees of freedom was seen to thermalize to $150\phantom{\rule{0.28em}{0ex}}\mathrm{mK}$. Based on the laser-cooled ${{\mathrm{C}}_{2}}^{\ensuremath{-}}$, a study on the sympathetic cooling of anions with masses 1--50 nucleon was performed, covering relevant candidates for investigations of chemical anion reactions at ultracold temperatures as well as for antimatter studies.

Physical Review A•Sep 13, 2017•10 citations

Laser-Assisted Evaporative Cooling of Anions

G. Cerchiari, P. Yzombard, A. Kellerbauer

We report the first cooling of atomic anions by laser radiation. O^{-} ions confined in a linear Paul trap were cooled by selectively photodetaching the hottest particles. For this purpose, anions with the highest total energy were illuminated with a 532 nm laser at their maximal radial excursion. Using laser-particle interaction, we realized a both colder and denser ion cloud, achieving a more than threefold temperature reduction from 1.15 to 0.33 eV. Compared with the interaction with a dilute buffer gas, the energy-selective addressing and removal of anions resulted in lower final temperatures, yet acted 10 times faster and preserved twice as large a fraction of ions in the final state. An ensemble of cold negative ions affords the ability to sympathetically cool any other negative ion species, enabling or facilitating a broad range of fundamental studies from interstellar chemistry to antimatter gravity. The technique can be extended to any negative ion species that can be neutralized via photodetachment.

Physical Review Letters•Sep 6, 2019•18 citations

Candidates for laser cooling of atomic anions: La − versus Os −

Lin Pan, Donald R. Beck

This brief report is a follow-up to the recent proposal to use La${}^{\ensuremath{-}}$ as another candidate, in addition to Os${}^{\ensuremath{-}}$, in laser cooling of anions, which can then be used to cool antiprotons sympathetically. Using the relativistic configuration interaction formalism, we calculate the photodetachment cross sections of the upper laser cooling state La${}^{\ensuremath{-}}$ $5d$$6{s}^{2}$$6p {}^{3}{D}_{1}$ and Os${}^{\ensuremath{-}}$ $5{d}^{6}$$6{s}^{2}$$6p {}^{6}{D}_{9/2}$. Our results show that La${}^{\ensuremath{-}}$ has a very similar two-photon detachment loss as Os${}^{\ensuremath{-}}$, retaining it as another promising candidate for cooling antiprotons sympathetically.

Physical Review A•Jul 6, 2010•32 citations

boron nitride anions

Breitmeier, Beke Leonie

This thesis presents the development and characterisation of an experimental setup designed for photodetachment spectroscopy of boron nitride anions (BN^-), as a step towards the long-term objective of laser cooling them. Laser cooling has become a mature and widely applied technique for neutral atoms and selected cationic molecular species, while its extension to anionic systems poses considerable experimental challenges. BN^- stands out as a promising candidate due to theoretical predictions of an electronic structure that features nearly diagonal Franck–Condon factors, suggesting the potential for closed optical cycling transitions—an essential prerequisite for laser cooling of molecular ions. Realising such a system would open new frontiers in precision spectroscopy, antimatter research, and ultracold chemistry involving negative ions. To this end, the setup—comprising a plasma discharge ion source with a piezoelectric valve, a Wiley–McLaren-type time-of-flight mass spectrometer, a channeltron ion detector, and an OPO laser—was calibrated using various negative and positive ion species, enabling accurate conversion of time-of-flight data into mass-to-charge spectra with sufficient resolution to identify light ions. Initial attempts at producing BN^- via thermal decomposition of ammonia borane (H_3B-NH_3) were conducted. While unambiguous detection of BN^- remains pending, several boron-containing positive and negative ions were observed. To validate the photodetachment capabilities of the setup, proof-of-principle depletion spectroscopy was performed on the well-characterised species O^-, OH^-, and O_2^- . Significant signal reductions were observed upon laser interaction at 450 nm for all species, and at 700 nm solely for O^- and O_2^- , consistent with their known photodetachment cross sections. To enable detection of neutral species resulting from photodetachment and to mimprove charged-neutral separation, a quadrupole bender was designed, simulated using SIMION, and successfully implemented in the setup. The overall system is now operational and provides a robust platform for forthcoming spectroscopic investigations of BN^- and related molecular anions, laying the groundwork for advancing laser-cooling techniques in negatively charged systems.

•Jan 1, 2025•0 citations

A novel cooling scheme for antiprotons

A. Kellerbauer, J. Walz

We propose a novel technique which uses laser-cooled negative osmium ions for sympathetic cooling of antiprotons. Temperatures down to the sub-millikelvin range might be achievable. These antiprotons could be used to form antihydrogen at ultra-cold temperatures, thus allowing efficient magnetic trapping of antihydrogen for high-resolution laser spectroscopy. Antihydrogen at sub-millikelvin temperatures might also enable first direct measurements of the gravitational acceleration of antimatter. Currently, no other technique exists which allows the cooling of large numbers of antiprotons to temperatures below that of the surrounding trap.

New Journal of Physics•Mar 29, 2006•66 citations
We propose to extend laser-cooling techniques, so far only achieved for neutral molecules, to molecular anions. A detailed computational study is performed for molecules stored in Penning traps using GPU based Monte Carlo simulations. Two cooling schemes—Doppler laser cooling and photodetachment cooling—are investigated. The sympathetic cooling of antiprotons is studied for the Doppler cooling scheme, where it is shown that cooling of antiprotons to subKelvin temperatures could becomes feasible, with impacts on the field of antimatter physics. The presented cooling schemes also have applications for the generation of cold, negatively charged particle sources and for the sympathetic cooling of other molecular anions.
We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_{2}^{-}, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped C_{2}^{-}, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.
We discuss the possibility of using optical dipole forces for Sisyphus cooling of ions stored in a Penning trap by addressing the specific case of the molecular cooling candidate ${{\mathrm{C}}_{2}}^{\ensuremath{-}}$. Using a GPU accelerated code for Penning trap simulations, which we extended to include the molecule-light interaction, we show that this scheme can decrease the time required for cooling by an order of magnitude with respect to Doppler cooling. In our simulation we found that a reduction of the axial anion temperature from 10K10\phantom{\rule{0.28em}{0ex}}\mathrm{K}10K to 50mK50\phantom{\rule{0.28em}{0ex}}\mathrm{mK}50mK in around 10s10\phantom{\rule{0.28em}{0ex}}\mathrm{s}10s is possible. The temperature of the radial degrees of freedom was seen to thermalize to 150mK150\phantom{\rule{0.28em}{0ex}}\mathrm{mK}150mK. Based on the laser-cooled ${{\mathrm{C}}_{2}}^{\ensuremath{-}}$, a study on the sympathetic cooling of anions with masses 1--50 nucleon was performed, covering relevant candidates for investigations of chemical anion reactions at ultracold temperatures as well as for antimatter studies.
We report the first cooling of atomic anions by laser radiation. O^{-} ions confined in a linear Paul trap were cooled by selectively photodetaching the hottest particles. For this purpose, anions with the highest total energy were illuminated with a 532 nm laser at their maximal radial excursion. Using laser-particle interaction, we realized a both colder and denser ion cloud, achieving a more than threefold temperature reduction from 1.15 to 0.33 eV. Compared with the interaction with a dilute buffer gas, the energy-selective addressing and removal of anions resulted in lower final temperatures, yet acted 10 times faster and preserved twice as large a fraction of ions in the final state. An ensemble of cold negative ions affords the ability to sympathetically cool any other negative ion species, enabling or facilitating a broad range of fundamental studies from interstellar chemistry to antimatter gravity. The technique can be extended to any negative ion species that can be neutralized via photodetachment.
This brief report is a follow-up to the recent proposal to use La${}^{\ensuremath{-}}$ as another candidate, in addition to Os${}^{\ensuremath{-}}$, in laser cooling of anions, which can then be used to cool antiprotons sympathetically. Using the relativistic configuration interaction formalism, we calculate the photodetachment cross sections of the upper laser cooling state La${}^{\ensuremath{-}}$ 5d5d5d6s26{s}^{2}6s26p3D16p {}^{3}{D}_{1}6p3D1​ and Os${}^{\ensuremath{-}}$ 5d65{d}^{6}5d66s26{s}^{2}6s26p6D9/26p {}^{6}{D}_{9/2}6p6D9/2​. Our results show that La${}^{\ensuremath{-}}$ has a very similar two-photon detachment loss as Os${}^{\ensuremath{-}}$, retaining it as another promising candidate for cooling antiprotons sympathetically.
This thesis presents the development and characterisation of an experimental setup designed for photodetachment spectroscopy of boron nitride anions (BN^-), as a step towards the long-term objective of laser cooling them. Laser cooling has become a mature and widely applied technique for neutral atoms and selected cationic molecular species, while its extension to anionic systems poses considerable experimental challenges. BN^- stands out as a promising candidate due to theoretical predictions of an electronic structure that features nearly diagonal Franck–Condon factors, suggesting the potential for closed optical cycling transitions—an essential prerequisite for laser cooling of molecular ions. Realising such a system would open new frontiers in precision spectroscopy, antimatter research, and ultracold chemistry involving negative ions. To this end, the setup—comprising a plasma discharge ion source with a piezoelectric valve, a Wiley–McLaren-type time-of-flight mass spectrometer, a channeltron ion detector, and an OPO laser—was calibrated using various negative and positive ion species, enabling accurate conversion of time-of-flight data into mass-to-charge spectra with sufficient resolution to identify light ions. Initial attempts at producing BN^- via thermal decomposition of ammonia borane (H_3B-NH_3) were conducted. While unambiguous detection of BN^- remains pending, several boron-containing positive and negative ions were observed. To validate the photodetachment capabilities of the setup, proof-of-principle depletion spectroscopy was performed on the well-characterised species O^-, OH^-, and O_2^- . Significant signal reductions were observed upon laser interaction at 450 nm for all species, and at 700 nm solely for O^- and O_2^- , consistent with their known photodetachment cross sections. To enable detection of neutral species resulting from photodetachment and to mimprove charged-neutral separation, a quadrupole bender was designed, simulated using SIMION, and successfully implemented in the setup. The overall system is now operational and provides a robust platform for forthcoming spectroscopic investigations of BN^- and related molecular anions, laying the groundwork for advancing laser-cooling techniques in negatively charged systems.
We propose a novel technique which uses laser-cooled negative osmium ions for sympathetic cooling of antiprotons. Temperatures down to the sub-millikelvin range might be achievable. These antiprotons could be used to form antihydrogen at ultra-cold temperatures, thus allowing efficient magnetic trapping of antihydrogen for high-resolution laser spectroscopy. Antihydrogen at sub-millikelvin temperatures might also enable first direct measurements of the gravitational acceleration of antimatter. Currently, no other technique exists which allows the cooling of large numbers of antiprotons to temperatures below that of the surrounding trap.