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Efficient three-dimensional sub-Doppler cooling of Ca+40 in a Penning trap

Brian J. McMahon* and Brian C. Sawyer

  • *Contact author: brian.mcmahon@gtri.gatech.edu
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Phys. Rev. A 114, 013119 – Published 20 July, 2026

DOI: https://doi.org/10.1103/qq69-zdy3

Abstract

We demonstrate efficient sub-Doppler laser cooling of the three eigenmodes of a Ca+40 ion confined in a compact Penning trap operating with a magnetic field of 0.91 T. Using the same set of laser beams as required for the initial Doppler laser cooling operation, we detune the laser frequencies to produce a narrow two-photon dark resonance. The process achieves a 1/e cooling time constant of 108(8)µs, ultimately reducing the mean thermal axial mode occupation from 72(23) to 1.5(3) in 800µs as measured by resonantly probing an electric quadrupole transition near 729 nm. A parametric drive is applied to the trap electrodes, which coherently exchanges the axial mode occupation with that of each radial mode, allowing for three-dimensional sub-Doppler cooling using only the axially propagating laser beams. This sub-Doppler cooling is achieved for an axial oscillation frequency of ωz=2π×221kHz, which places the motion well outside the Lamb-Dicke confinement regime at the Doppler laser cooling limit. Our measured cooling rate and final mode occupation are in good agreement with a semiclassical model which combines a Lindblad master equation solution for ion-photon interactions with classical harmonic-oscillator motion of the trapped ion.

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Phys. Rev. A 114, 013119– Published 20 July, 2026
  • Received 13 February 2026
  • Accepted 24 April 2026
Article part of CHORUS
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