Scalable microchip ion traps and guides for cold molecular ions

Sympathetic cooling and Coulomb crystallisation of molecular ions above the
surface of an ion-trap chip were demonstrated. N2+ and CaH+ ions were confined
in a surface-electrode radiofrequency ion trap and cooled by the interaction
with laser-cooled Ca+ ions to secular translational temperatures in the
milliKelvin range. The configuration of trapping potentials generated by the surface
electrodes enabled the formation of planar bicomponent Coulomb crystals
and the spatial separation of the molecular from the atomic ions. The structural
and thermal properties of the crystals were characterized using molecular
dynamics simulations. The effects of trap anharmoncities on the shape and
energy of bicomponent crystals were theoretically investigated. It was shown
that the trapping potentials can also deliberately be engineered to spatially
separate ion species in bicomponent crystals. Furthermore, a multi-functional
surface-electrode radiofrequency ion-trap chip has been developed to enable experiments
with cold molecular ions using a monolithic device. The chip was
designed to combine various tasks such as loading and preparation of ions, mass
spectrometry, spectroscopy, reaction studies, and manipulation of ion crystals
in a miniaturised device. This chip features carefully engineered ion channel
intersections that enable transporting sympathetically cooled molecular ions in
the form of bicomponent crystals. A detailed description of the fabrication and
simulation of the two chips are presented. The present study extends chipbased
trapping techniques to Coulomb-crystallised molecular ions with potential
applications in mass spectrometry, cold chemistry, quantum technology, and
spectroscopy.