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arXiv · 1705.08518

Sideband cooling of small ion Coulomb crystals in a Penning trap

G. Stutter·P. Hrmo·V. Jarlaud·M. K. Joshi·J. F. Goodwin·R. C. Thompson
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Abstract

We have recently demonstrated the laser cooling of a single $^{40}$Ca$^+$ ion to the motional ground state in a Penning trap using the resolved-sideband cooling technique on the electric quadrupole transition S$_{1/2} \leftrightarrow$ D$_{5/2}$. Here we report on the extension of this technique to small ion Coulomb crystals made of two or three $^{40}$Ca$^+$ ions. Efficient cooling of the axial motion is achieved outside the Lamb-Dicke regime on a two-ion string along the magnetic field axis as well as on two- and three-ion planar crystals. Complex sideband cooling sequences are required in order to cool both axial degrees of freedom simultaneously. We measure a mean excitation after cooling of $\bar n_\text{COM}=0.30(4)$ for the centre of mass mode and $\bar n_\text{B}=0.07(3)$ for the breathing mode of the two-ion string with corresponding heating rates of 11(2) s$^{-1}$ and 1(1) s$^{-1}$ at a trap frequency of 162 kHz. The ground state occupation of the axial modes is above 75% for the two-ion planar crystal and the associated heating rates 0.8(5) s$^{-1}$ at a trap frequency of 355 kHz.

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G. Stutter, P. Hrmo, V. Jarlaud, M. K. Joshi, J. F. Goodwin, R. C. Thompson. 2017-05-23. Sideband cooling of small ion Coulomb crystals in a Penning trap. https://doi.org/10.1080/09500340.2017.1376719

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