Cooling of atomic motion is a crucial tool for many branches of atomic physics, ranging from fundamental physics explorations to quantum information and sensing. For trapped ions, electromagnetically-induced-transparency (EIT) cooling has received attention for the relative speed, low laser power requirements, and broad cooling bandwidth of the technique. However, in applications where the ion used for cooling has hyperfine structure to enable long coherence times, it is difficult to find a closed three-level system in which to perform standard EIT cooling. Here, we demonstrate successful EIT cooling on
25Mg+ by the addition of an extra laser frequency; this method can be applied to any ion with nonzero nuclear spin. Furthermore, we simultaneously EIT cool all axial modes in mixed-species crystals $^{9}\mathrm{Be}^{+}\text{\ensuremath{-}}^{25}\mathrm{Mg}^{+}$ and $^{9}\mathrm{Be}^{+}\text{\ensuremath{-}}^{25}\mathrm{Mg}^{+}\text{\ensuremath{-}}^{9}\mathrm{Be}^{+}$ through the
25Mg+ ion. This demonstrates the viability of EIT cooling in architectures where the laser-cooled species can host high-fidelity hyperfine qubits.
Electromagnetically induced transparency (EIT) can be used to cool an atom in a harmonic potential close to the ground state by addressing several vibrational modes simultaneously. Previous experimental efforts focus on trapped ions and neutral atoms in a standing wave trap. In this work, we demonstrate EIT cooling of an optically trapped single neutral atom, where the trap frequencies are an order of magnitude smaller than in an ion trap and a standing wave trap. We resolve the Fano resonance feature in fluorescence excitation spectra and the corresponding cooling profile in temperature measurements. A final temperature of around 6 µK is achieved with EIT cooling, a factor of 2 lower than the previous value obtained using polarization gradient cooling. Published by the American Physical Society 2024