Experiments with antihydrogen (H[over ¯]) for a study of matter-antimatter symmetry and antimatter gravity require ultracold H[over ¯] to reach ultimate precision. A promising path towards antiatoms much colder than a few kelvin involves the precooling of antiprotons by laser-cooled anions. Because of the weak binding of the valence electron in anions-dominated by polarization and correlation effects-only few candidate systems with suitable transitions exist. We report on a combination of experimental and theoretical studies to fully determine the relevant binding energies, transition rates, and branching ratios of the most promising candidate La^{-}. Using combined transverse and collinear laser spectroscopy, we determined the resonant frequency of the laser cooling transition to be ν=96.592 713(91) THz and its transition rate to be A=4.90(50)×10^{4} s^{-1}. Using a novel high-precision theoretical treatment of La^{-} we calculated yet unmeasured energy levels, transition rates, branching ratios, and lifetimes to complement experimental information on the laser cooling cycle of La^{-}. The new data establish the suitability of La^{-} for laser cooling and show that the cooling transition is significantly stronger than suggested by a previous theoretical study.Experiments with antihydrogen (H[over ¯]) for a study of matter-antimatter symmetry and antimatter gravity require ultracold H[over ¯] to reach ultimate precision. A promising path towards antiatoms much colder than a few kelvin involves the precooling of antiprotons by laser-cooled anions. Because of the weak binding of the valence electron in anions-dominated by polarization and correlation effects-only few candidate systems with suitable transitions exist. We report on a combination of experimental and theoretical studies to fully determine the relevant binding energies, transition rates, and branching ratios of the most promising candidate La^{-}. Using combined transverse and collinear laser spectroscopy, we determined the resonant frequency of the laser cooling transition to be ν=96.592 713(91) THz and its transition rate to be A=4.90(50)×10^{4} s^{-1}. Using a novel high-precision theoretical treatment of La^{-} we calculated yet unmeasured energy levels, transition rates, branching ratios, and lifetimes to complement experimental information on the laser cooling cycle of La^{-}. The new data establish the suitability of La^{-} for laser cooling and show that the cooling transition is significantly stronger than suggested by a previous theoretical study.

arXiv:1712.08275Physical Review LettersMar 28, 201838 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.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 AJul 6, 201032 citations

High-precision calculation of La

^-

atomic properties for anion laser cooling

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.