Laser cooling of mechanical degrees of freedom is one of the most significant achievements in the field of optomechanics. Here, we report, for the first time to the best of our knowledge, efficient passive optomechanical cooling of the motion of a freestanding waveguide coupled to a whispering-gallery-mode (WGM) resonator. The waveguide is an 8 mm long glass-fiber nanospike, which has a fundamental flexural resonance at Ω/2π=2.5 kHz and a Q-factor of 1.2×105. Upon launching ∼250 μW laser power at an optical frequency close to the WGM resonant frequency, we observed cooling of the nanospike resonance from room temperature down to 1.8 K. Simultaneous cooling of the first higher-order mechanical mode is also observed. The strong suppression of the overall Brownian motion of the nanospike, observed as an 11.6 dB reduction in its mean square displacement, indicates strong optomechanical stabilization of linear coupling between the nanospike and the cavity mode. The cooling is caused predominantly by a combination of photothermal effects and optical forces between nanospike and WGM resonator. The results are of direct relevance in the many applications of WGM resonators, including atom physics, optomechanics, and sensing.

中文翻译：

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耦合到回音壁模式谐振器的波导的光机械冷却和自稳定

机械自由度的激光冷却是光机械领域最重要的成就之一。在这里，我们据我们所知，首次报告了耦合到回音壁模式 (WGM) 谐振器的独立波导运动的高效被动光机械冷却。波导是一个 8 毫米长的玻璃纤维纳米尖峰，它在 Ω/2π=2.5 kHz 和 Q 因子为 1.2×105 时具有基本弯曲共振。在以接近 WGM 共振频率的光频率发射 ~250 μW 激光功率后，我们观察到纳米尖峰共振从室温冷却到 1.8 K。还观察到第一高阶机械模式的同时冷却。纳米尖峰的整体布朗运动的强烈抑制，观察为 11。均方位移减少 6 dB，表明纳米尖峰和腔模之间的线性耦合具有很强的光机械稳定性。冷却主要是由纳米尖峰和 WGM 谐振器之间的光热效应和光学力的组合引起的。结果与 WGM 谐振器的许多应用直接相关，包括原子物理学、光机械学和传感。