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Physical Review A

Planar Coulomb bicrystals

I. M. Buluta, Shuichi Hasegawa

Published Oct 31, 2008• 11 citations
Publisher

Abstract

We numerically studied two-component planar Coulomb crystals (planar bicrystals) in rf traps. The number of ions in the inner shell was found to be limited by the mass difference between the two components and we calculated the maximum possible number of ions in the inner shells for various mass ratios. When large axial potentials are applied the spatial separation between components depends on the trapping parameters as well as on the ion masses and charges. We derived the spatial separation both theoretically and numerically and discussed its effect on the efficiency of sympathetic cooling and on rf heating. We suggest using planar bicrystals for implementing quantum simulation and computation.

DOI
10.1103/physreva.78.042340

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Cold molecular ions are of great interest for applications in cold collision studies, chemistry, precision spectroscopy and quantum technologies. In this context, sympathetic cooling of molecular ions by the interaction with laser-cooled atomic ions is a powerful method to cool their translational motion and achieve translational temperatures in the millikelvin range. Recently, we implemented this method in a surface-electrode ion trap. The flexibility in shaping the trapping potentials offered by the surface-electrode structure enabled us to generate planar bicomponent Coulomb crystals and spatially separate the molecular from the atomic ions. Here, we present a detailed description of the fabrication and simulation of the trap as well as a theoretical and experimental investigation of the structural and energetic properties of the Coulomb crystals obtained in the device. We discuss in more detail the separation of different ion species using static electric fields and explore the effects of trap anharmoncities on the shape of bicomponent crystals.
Linear strings of trapped atomic ions held in radio-frequency (rf) traps constitute one of the leading platforms for quantum simulation experiments, allowing the investigation of interacting quantum matter.However, linear ion strings have drawbacks, such as the difficulty of scaling beyond approximately 50 particles as well as the inability to naturally implement spin models with more than one spatial dimension.Here we present experiments with planar Coulomb crystals of up to 105 40 Ca + ions in a novel monolithic rf trap, laying the groundwork for quantum simulations of two-dimensional spin models with singleparticle control.We characterize the trapping potential by analysis of crystal images and compare the observed crystal configurations with numerical simulations.We further demonstrate stable confinement of large crystals, free of structural configuration changes, and find that rf heating of the crystal is not an obstacle for future quantum simulation experiments.Finally, we prepare the out-of-plane motional modes of planar crystals consisting of up to 105 ions close to their ground state by electromagnetically induced transparency cooling, an important prerequisite for implementing long-range entangling interactions.
We report the sympathetic cooling and Coulomb crystallization of molecular ions above the surface of an ion-trap chip. N2+{\mathrm{N}}_{2}^{+}N2+​ and CaH+{\mathrm{CaH}}^{+}CaH+ ions were confined in a surface-electrode radio-frequency (rf) ion trap and cooled by the interaction with laser-cooled Ca+{\mathrm{Ca}}^{+}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 on the chip. The structural and thermal properties of the Coulomb crystals were characterized using molecular dynamics simulations. The present study extends chip-based trapping techniques to cold molecular ions with potential applications in mass spectrometry, chemistry, quantum information science, and spectroscopy.