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Coulomb crystallization of xenon highly charged ions in a laser-cooled Ca+ matrix

Leonid Prokhorov, Aaron A. Smith, Mingyao Xu, Kostas Georgiou, Vera Guarrera, Lakshmi P. Kozhiparambil Sajith, Elwin A. Dijck, Christian Warnecke, Malte Wehrheim, Alexander Wilzewski, Laura Blackburn, Matthias Keller, Vincent Boyer, Thomas Pfeifer, Ullrich Schwanke, Cigdem Issever, Steven Worm, Piet O. Schmidt, José R. Crespo Lopez-Urrutia, Giovanni Barontini

Abstract

We report on the sympathetic cooling and Coulomb crystallization of xenon highly charged ions (HCIs) with laser-cooled Ca$^+$ ions. The HCIs are produced in a compact electron beam ion trap, then charge selected, decelerated, and finally injected into a cryogenic linear Paul trap. There, they are captured into $^{40}$Ca$^+$ Coulomb crystals, and co-crystallized within them, causing dark voids in their fluorescence images. Fine control over the number of trapped ions and HCIs allows us to realize mixed-species crystals with arbitrary ordering patterns. By investigating Xe$^{q+}$--Ca$^+$ strings, we confirm the HCI charge states, measure their lifetime and characterize the mixed-species motional modes. Our system effectively combines the established quantum control toolbox for Ca$^+$ with the rich set of atomic properties of Xe highly charged ions, providing a resourceful platform for optical frequency metrology, searches for signatures of new physics, and quantum information science.

Coulomb crystallization of xenon highly charged ions in a laser-cooled Ca+ matrix

Abstract

We report on the sympathetic cooling and Coulomb crystallization of xenon highly charged ions (HCIs) with laser-cooled Ca ions. The HCIs are produced in a compact electron beam ion trap, then charge selected, decelerated, and finally injected into a cryogenic linear Paul trap. There, they are captured into Ca Coulomb crystals, and co-crystallized within them, causing dark voids in their fluorescence images. Fine control over the number of trapped ions and HCIs allows us to realize mixed-species crystals with arbitrary ordering patterns. By investigating Xe--Ca strings, we confirm the HCI charge states, measure their lifetime and characterize the mixed-species motional modes. Our system effectively combines the established quantum control toolbox for Ca with the rich set of atomic properties of Xe highly charged ions, providing a resourceful platform for optical frequency metrology, searches for signatures of new physics, and quantum information science.

Paper Structure

This paper contains 1 section, 1 equation, 4 figures.

Table of Contents

  1. Acknowledgements

Figures (4)

  • Figure 1: a) Schematics of the main in-vacuo components of our apparatus, including the compact EBIT, the beam line, and the science chamber (relative distances are not to scale). The science chamber has concentric room temperature, 40 K, and 4 K stages, with the cryogenic Paul trap at the center. Arrows show the ionization and cooling lasers, and the Ca atomic beam injection into the cryogenic region. b) Typical time-of-flight spectrum of Xe HCIs as observed on microchannel plate 1. Large peaks correspond to the labelled ionization states, and smaller features to different stable isotopes of Xe. c) Points display the amplitude of the signal of charge-selected Xe$^{11+}$ ions on microchannel plate 2 as a function of the voltage of the retarding field analyser, with a fitted line using an error function. This fit yields a central energy of $\simeq$161 $q$ eV, where $q$ is the charge state, and a full-width-at-half-maximum of $\simeq$12.6 $q$ eV. This microchannel plate can be moved out to allow the HCIs to reach the science chamber. d-f) Fluorescence images of Ca$^+$ Coulomb crystals with 1, 3 and 4 Xe$^{11+}$ HCI implanted, respectively. g) the same as d) but with one Xe$^{19+}$ HCI crystallized. All exposure times are 1 s. For single Ca$^+$ ion we measure trapping frequencies of $(\omega_x,\omega_y,\omega_z)=2\pi\times(821, 844,234)$ kHz, respectively.
  • Figure 2: a) Fluorescence images of a mixed-species Coulomb crystal containing seven Xe$^{11+}$ HCIs, each manifesting as a void in the crystalline structure. b) and c) Mixed-species Coulomb crystals with four Xe$^{11+}$ HCIs and different numbers of Ca$^+$ ions. d)-f) The same but with three Xe$^{11+}$ HCIs. The exposure time for all panels is 1 s.
  • Figure 3: a) Fluorescence image of a mixed-species Coulomb crystal containing one Ca$^+$ ion (the purple dot) and one Xe$^{11+}$ HCI (not visible). b-g) the same as a) but with two to four Ca$^+$ ions. h) The circles are the measured frequencies of the two lower axial modes of the crystals shown in a)-g), where X$\equiv$Xe$^{11+}$ and C$\equiv$Ca$^{+}$. The errorbars are smaller than the size of the circles. The crosses are the values calculated with the method explained in the text. The dashed line is the measured secular axial frequency for Ca$^+$ in the same trap.
  • Figure :