Laser Cooling of Radium Ions

Abstract

The unstable radium nucleus is appealing for probing new physics due to its high mass, octupole deformation and energy level structure. Ion traps, with long hold times and low particle numbers, are excellent for work with radioactive species, such as radium and radium-based molecular ions, where low activity, and hence low total numbers, is desirable. We address the challenges associated with the lack of stable isotopes in a tabletop experiment with a low-activity ($\sim 10\mu \mathrm{Ci}$) source where we laser-cool trapped radium ions. With a laser-cooled radium ion we measured the $7p{}^2{P}_{1/2}^o$ state's branching fractions to the ground state, $7s{}^2{S}_{1/2}$, and a metastable excited state, $6d{}^2{D}_{3/2}$, to be $p=0.9104(7)$ and $0.0896(7)$, respectively. With a nearby tellurium reference line we measured the $7s{}^2{S}_{1/2}\to 7p{}^2{P}_{1/2}^o$ transition frequency, 640.09663(6) THz.

arXiv comment5 pages, 4 figures

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• Opportunities for Fundamental Physics Research with Radioactive Molecules
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• Beyond the charge radius: the information content of the fourth radial moment
• Optical Mass Spectrometry of Cold ${\mathrm{RaOH}}^{+}$ and ${{\mathrm{RaOCH}}_3}^{+}$
• Radium Ion Optical Clock
• Second-Scale Coherence Measured at the Quantum Projection Noise Limit with Hundreds of Molecular Ions
• Measurements of the branching ratios for $6P_{1/2}$ decays in ${}^{138}$Ba${}^{+}$
• The hyperfine anomaly in heavy atoms and its role in precision atomic searches for new physics
• Electric dipole transition amplitudes for atoms and ions with one valence electron
• Measurements of electric quadrupole transition frequencies in ${}^{226}$Ra${}^{+}$
• Measurements and analysis of response function of cold atoms in optical molasses
• Measurement of the $7p{}^2{P}_{3/2}$ state branching fractions in ${\mathrm{Ra}}^{+}$
• Dipole-phonon quantum logic with alkaline-earth monoxide and monosulfide cations
• Laser cooling and trapping of ${}^{224}$Ra${}^{+}$
• Direct measurement of the $7s{}^2{S}_{1/2}\to$ $7p{}^2{P}_{3/2}$ transition frequency in ${}^{226}$Ra${}^{+}$
• Theoretical characterisation of the barium II and radium II ions
• Molecular laser cooling using serrodynes: Implementation, characterization and prospects
• Lifetimes of the Metastable $6\mathrm{d}{}^2{\mathrm{D}}_{5/2}$ and $6\mathrm{d}{}^2{\mathrm{D}}_{3/2}$ States of Ra${}^{+}$
• Spectroscopy of electric dipole and quadrupole transitions in ${}^{224}$Ra${}^{+}$
• Laser Cooling and Hyperfine Measurements of Radium-225 Ions