Sympathetic cooling and detection of a hot trapped ion by a cold one

Abstract

We investigate the dynamics of an ion sympathetically cooled by another laser-cooled ion or small ion crystal. To this end, we develop simple models of the cooling dynamics in the limit of weak Coulomb interactions. Experimentally, we create a two-ion crystal of Ca${}^{+}$ and Al${}^{+}$ by photo-ionization of neutral atoms produced by laser ablation. We characterize the velocity distribution of the laser-ablated atoms crossing the trap by time-resolved fluorescence spectroscopy. We observe neutral atom velocities much higher than the ones of thermally heated samples and find as a consequence long sympathethic cooling times before crystallization occurs. Our key result is a new technique for detecting the loading of an initially hot ion with energy in the eV range by monitoring the motional state of a Doppler-cooled ion already present in the trap. This technique not only detects the ion but also provides information about dynamics of the sympathetic cooling process.

23 pages, 10 figures, small corrections and extensions in response to referee comments

References in corpus (6)

• Ion-trap measurements of electric-field noise near surfaces
• Complete methods set for scalable ion trap quantum information processing
• Fluorescence during Doppler cooling of a single trapped atom
• Laser ablation loading of a surface-electrode ion trap
• Translational cooling and storage of protonated proteins in an ion trap at subkelvin temperatures
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