Cooling the motion of trapped ions to near the quantum ground state is crucial for many applications in quantum information processing and quantum metrology. However, certain motional modes of trapped-ion crystals can be difficult to cool due to weak or zero interaction between the modes and the cooling radiation, typically laser beams. We overcome this challenge by coupling a mode that interacts weakly with cooling radiation to one that interacts strongly with cooling radiation using parametric modulation of the trapping potential, thereby enabling indirect cooling of the weakly interacting mode. In this way, we demonstrate near-ground-state cooling of motional modes with weak or zero cooling radiation interaction in multi-ion crystals of the same and mixed ion species, specifically ${}^9{\mathrm{Be}}^{+}\text{−}{}^9{\mathrm{Be}}^{+}$, ${}^9{\mathrm{Be}}^{+}\text{−}{}^{25}{\mathrm{Mg}}^{+}$, and ${}^9{\mathrm{Be}}^{+}\text{−}{}^{25}{\mathrm{Mg}}^{+}\text{−}{}^9{\mathrm{Be}}^{+}$ crystals. This approach can be generally applied to any Coulomb crystal where certain motional modes cannot be directly cooled efficiently, including crystals containing molecular ions, highly charged ions, charged fundamental particles, or charged macroscopic objects.

中文翻译：

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弱耦合俘获离子机械振荡器的间接冷却

将捕获离子的运动冷却到接近量子基态对于量子信息处理和量子计量中的许多应用至关重要。然而，俘获离子晶体的某些运动模式可能难以冷却，因为这些模式与冷却辐射（通常是激光束）之间的相互作用较弱或为零。我们通过使用捕获势的参数调制将与冷却辐射弱相互作用的模式耦合到与冷却辐射强相互作用的模式来克服这一挑战，从而实现弱相互作用模式的间接冷却。通过这种方式，我们证明了在相同和混合离子种类的多离子晶体中具有弱或零冷却辐射相互作用的运动模式的近基态冷却，特别是${}^9{是}^{+}\text{-}{}^9{是}^{+}$,${}^9{是}^{+}\text{-}{}^{25}{镁}^{+}$， 和${}^9{是}^{+}\text{-}{}^{25}{镁}^{+}\text{-}{}^9{是}^{+}$晶体。这种方法通常可以应用于某些运动模式无法直接有效冷却的任何库仑晶体，包括含有分子离子、高电荷离子、带电基本粒子或带电宏观物体的晶体。