Tuning nonthermal to thermal distributions in time-dependent Paul traps.

Haggai Landa

Published Sep 27, 2018• 0 citations

Abstract

We study the probability distribution of an atomic ion being laser-cooled in a radio-frequency Paul trap, in terms of Hamiltonian action-angle coordinates appropriate for the time-dependent potential. Close to the effective minimum in many Paul traps, the periodically-driven potential is approximately quadratic in the coordinates. We find that despite the microscopic nonequilibrium forces, a stationary thermal-like exponential distribution in the action is reached after coarse-graining the angles, with a mean action corresponding to the Doppler cooling limit. However, residual electric fields can push the ion from the origin of the quadrupole potential and set it into a large-amplitude oscillation. Above a threshold amplitude of such excess micromotion, the action distribution for motion expanded about the driven oscillation broadens and becomes distinctly nonthermal. We find that by a proper choice of the laser detuning the distribution can be made exponential again, with a mean action close to the Doppler cooling limit. This is important for quantum information processing and other applications, and in particular the derived approach can be immediately applied to crystals of trapped ions in planar configurations, where the driven motion of ions is unavoidable.

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