Radio-frequency sideband cooling and sympathetic cooling of trapped ions in a static magnetic field gradient

Abstract

We report a detailed investigation on near-ground state cooling of one and two trapped atomic ions. We introduce a simple sideband cooling method for confined atoms and ions, using RF radiation applied to bare ionic states in a static magnetic field gradient, and demonstrate its application to ions confined at secular trap frequencies, ${\omega }_z\approx 2\pi \times 117$kHz. For a single \ybplus ion, the sideband cooling cycle reduces the average phonon number, $⟨n⟩$ from the Doppler limit to $⟨n⟩=$ 0.30(12). This is in agreement with the theoretically estimated lowest achievable phonon number in this experiment. We extend this method of RF sideband cooling to a system of two \ybplus ions, resulting in a phonon number of $⟨n⟩=$ 1.1(7) in the center-of-mass mode. Furthermore, we demonstrate the first realisation of sympathetic RF sideband cooling of an ion crystal consisting of two individually addressable identical isotopes of the same species.

8 pages, 7 figures

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