Careful control of quantum states is a gateway to research in many areas of science such as quantum information, quantum-controlled chemistry, and astrophysical processes. Precise optical control of molecular ions remains a challenge due to the scarcity of suitable level schemes, and direct laser cooling has not yet been achieved for either positive or negative molecular ions. Using a cryogenic wire trap, we show how the internal quantum states of ${\mathrm{C}}_{2}^{\ensuremath{-}}$ anions can be manipulated using optical pumping and inelastic quenching collisions with ${\mathrm{H}}_{2}$ gas. We obtained optical pumping efficiencies of about 96% into the first vibrational level of ${\mathrm{C}}_{2}^{\ensuremath{-}}$ and determined the absolute inelastic rate coefficient from $v=1$ to 0 to be ${k}_{\mathrm{q}}=(3.2\ifmmode\pm\else\textpm\fi{}{0.2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1.3}_{\mathrm{sys}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$ at 20(3) K, over 3 orders of magnitude smaller than the capture limit. Reduced-dimensional quantum scattering calculations yield a small rate coefficient as well, but significantly larger than the experimental value. Using optical pumping and inelastic collisions, we also realized fluorescence imaging of negative molecular ions. Our work demonstrates high control of a cold ensemble of ${\mathrm{C}}_{2}^{\ensuremath{-}}$, providing a solid foundation for future work on laser cooling of molecular ions.Careful control of quantum states is a gateway to research in many areas of science such as quantum information, quantum-controlled chemistry, and astrophysical processes. Precise optical control of molecular ions remains a challenge due to the scarcity of suitable level schemes, and direct laser cooling has not yet been achieved for either positive or negative molecular ions. Using a cryogenic wire trap, we show how the internal quantum states of ${\mathrm{C}}_{2}^{\ensuremath{-}}$ anions can be manipulated using optical pumping and inelastic quenching collisions with ${\mathrm{H}}_{2}$ gas. We obtained optical pumping efficiencies of about 96% into the first vibrational level of ${\mathrm{C}}_{2}^{\ensuremath{-}}$ and determined the absolute inelastic rate coefficient from $v=1$ to 0 to be ${k}_{\mathrm{q}}=(3.2\ifmmode\pm\else\textpm\fi{}{0.2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1.3}_{\mathrm{sys}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$ at 20(3) K, over 3 orders of magnitude smaller than the capture limit. Reduced-dimensional quantum scattering calculations yield a small rate coefficient as well, but significantly larger than the experimental value. Using optical pumping and inelastic collisions, we also realized fluorescence imaging of negative molecular ions. Our work demonstrates high control of a cold ensemble of ${\mathrm{C}}_{2}^{\ensuremath{-}}$, providing a solid foundation for future work on laser cooling of molecular ions.

Physical Review LettersOct 30, 20239 citations

Demonstration of internal state laser cooling of molecular ions

T. Schneider, Bernhard Roth, Michael G. Hansen +5 more

This study demonstrates an all-optical internal state cooling scheme for HD+molecular ions in the rovibrational ground state using a 5.484 mum cw-quantum cascade laser. Resonance-enhanced multi-photon dissociation is used to selectively remove the ground-state HD+ions from the trap. The efficiency of the pumping scheme is investigated by comparing the corresponding changes in fluorescence with and without an optical pumping phase preceding the detection. An increase in the relative fluorescence decay by a factor of 3 is observed with optical pumping.This study demonstrates an all-optical internal state cooling scheme for HD+molecular ions in the rovibrational ground state using a 5.484 mum cw-quantum cascade laser. Resonance-enhanced multi-photon dissociation is used to selectively remove the ground-state HD+ions from the trap. The efficiency of the pumping scheme is investigated by comparing the corresponding changes in fluorescence with and without an optical pumping phase preceding the detection. An increase in the relative fluorescence decay by a factor of 3 is observed with optical pumping.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)Jun 1, 20090 citations

Towards quantum control of molecular ions

David Hanneke, Edward Kleiner, Alexander Frenett

Bulletin of the American Physical SocietyMay 24, 20160 citations

Quantum State Control of Trapped Atomic and Molecular Ions

Christopher M. Seck

Jan 1, 20160 citations

Toward Rotational Cooling of Trapped SiO+ by Optical Pumping

David Tabor

This thesis presents a scheme for preparation of trapped molecular ions with a high degree of internal state purity by optical pumping with a broadband pulse-shaped femtosecond laser; the internal structure of SiO+ permits fast stepwise pumping through the tens of rotational levels populated in a room-temperature distribution. Two analyses, which guided the experimental implementation, are presented: (1) a novel method of quantifying anharmonicity in the trapping potentials, which limits the number of ions that can be trapped, and (2) a rate-equation simulation of the quantum state evolution during pumping. Experimental implementation of pulse shaping and its characterization are discussed, as is the molecular spectroscopy used to reference this light to the rotational cooling transitions. Internal state analysis can be performed using resonance enhanced multiphoton dissociation.This thesis presents a scheme for preparation of trapped molecular ions with a high degree of internal state purity by optical pumping with a broadband pulse-shaped femtosecond laser; the internal structure of SiO+ permits fast stepwise pumping through the tens of rotational levels populated in a room-temperature distribution. Two analyses, which guided the experimental implementation, are presented: (1) a novel method of quantifying anharmonicity in the trapping potentials, which limits the number of ions that can be trapped, and (2) a rate-equation simulation of the quantum state evolution during pumping. Experimental implementation of pulse shaping and its characterization are discussed, as is the molecular spectroscopy used to reference this light to the rotational cooling transitions. Internal state analysis can be performed using resonance enhanced multiphoton dissociation.

Jan 1, 20140 citations

{\mathrm{H}}_{2}

gas. We obtained optical pumping efficiencies of about 96% into the first vibrational level of ${\mathrm{C}}_{2}^{\ensuremath{-}}$ and determined the absolute inelastic rate coefficient from

v=1

to 0 to be ${k}_{\mathrm{q}}=(3.2\ifmmode\pm\else\textpm\fi{}{0.2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1.3}_{\mathrm{sys}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$ at 20(3) K, over 3 orders of magnitude smaller than the capture limit. Reduced-dimensional quantum scattering calculations yield a small rate coefficient as well, but significantly larger than the experimental value. Using optical pumping and inelastic collisions, we also realized fluorescence imaging of negative molecular ions. Our work demonstrates high control of a cold ensemble of ${\mathrm{C}}_{2}^{\ensuremath{-}}$, providing a solid foundation for future work on laser cooling of molecular ions.