We demonstrate rotational cooling of the silicon monoxide cation via optical pumping by a spectrally filtered broadband laser. Compared with diatomic hydrides, SiO+ is more challenging to cool because of its smaller rotational interval. However, the rotational level spacing and large dipole moment of SiO+ allows direct manipulation by microwaves, and the absence of hyperfine structure in its dominant isotopologue greatly reduces demands for pure quantum state preparation. These features make ${}^{28}$Si${}^{16}$O+ a good candidate for future applications such as quantum information processing. Cooling to the ground rotational state is achieved on a 100 ms time scale and attains a population of 94(3)%, with an equivalent temperature $T=0.53(6)$ K. We also describe a novel spectral-filtering approach to cool into arbitrary rotational states and use it to demonstrate a narrow rotational population distribution ($N\pm 1$) around a selected state.

中文翻译：

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将零核自旋分子离子冷却到选定的旋转状态

我们展示了通过光谱过滤宽带激光器的光泵浦对一氧化硅阳离子的旋转冷却。与双原子氢化物相比，SiO +由于其较小的旋转间隔而具有更大的冷却难度。然而，SiO +的旋转能级间距和大偶极矩允许通过微波直接操作，并且在其主要的同位素异构体中不存在超精细结构，大大降低了对纯量子态制备的需求。这些功能使${}^{28}$硅${}^{16}$O +是诸如量子信息处理等未来应用的良好选择。在100毫秒的时间范围内冷却到地面旋转状态，并且在等效温度下达到94（3）％的填充量$Ť=0.53（6）$ K。我们还描述了一种新颖的光谱过滤方法，可以冷却到任意旋转状态，并用它来证明狭窄的旋转种群分布（$ñ\pm \mathrm{1个}$）周围的选定状态。