We have cooled ensembles of the molecular hydrogen ions H2+, H3+, and all their deuterated variants to temperatures of a few mK in a radio frequency trap, by sympathetic cooling with laser-cooled beryllium ions. The molecular ions are embedded in the central regions of Coulomb crystals. Mass spectroscopy and molecular dynamics simulations were used to accurately characterize the properties of the ultracold multispecies crystals. We demonstrate species-selective purification of multispecies ensembles. These molecules are of fundamental importance as the simplest of all molecules, and have the potential to be used for precision tests of molecular structure theory, tests of Lorentz invariance, and measurements of electron to nuclear mass ratios and their time variation.
We investigate the coupling between motional resonances of translationally cold ͑10 mK range͒ atomic and molecular ions in multispecies Coulomb crystals, stored in a linear Paul trap. The atomic and molecular ions were sympathetically cooled by laser-cooled Be + ions. The motional resonances of the different ion species were determined nondestructively with high mass-to-charge resolution upon excitation with an oscillating electric field. The experimental results show good agreement with results from molecular dynamics simulations and allow for a precise identification of sympathetically cooled particles in multispecies ion crystals.
Optical frequency standards based on narrow absorptions in laser-cooled single trapped ions have recently begun to demonstrate stabilities that are competitive with cold atom fountain microwave standards. This paper presents a short review of the wider state-of-the-art development of these single cold trapped ion frequency standards, coupled with a more detailed account of recent results achieved at National Physical Laboratory in respect of single ion systems based on 88 Sr + , 87 Sr + and 171 Yb + . Narrow linewidth data for the optical clock quadrupole and octupole transitions respectively at 674 nm in 88 Sr + and 467 nm in 171 Yb + , are presented, together with a discussion of current systematics and future projections. The potential for optical clock operation is outlined.
Chemical reactions between ultracold 9 Be + ions and room-temperature molecular hydrogen isotopomers and between ultracold H 3 + ions and room-temperature O 2 have been studied in a laser-cooling ion trap apparatus. For small Coulomb crystals of beryllium ions, reactions can be followed at the single-ion level. We demonstrate characterization of a chemical reaction in which neither one of the reactants nor the product is directly detectable. In this case molecular dynamics simulations were used for the determination of ion numbers from images of the 9 Be + ion ensemble. The observed reaction rates are in agreement with the Langevin ion-neutral reaction theory.
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