The optical lever is a centuries old and widely used detection technique employed in applications ranging from consumer products and industrial sensors to precision force microscopes used in scientific research. However, despite the long history, its quantum limits have yet to be explored. In general, any precision optical measurement is accompanied by optical force induced disturbance to the measured object (termed as back action) leading to a standard quantum limit (SQL). Here, we give a simple ray optics description of how such back action can be evaded in optical lever detection. We perform a proof-of-principle experiment demonstrating the mechanism of back action evasion in the classical regime, by developing a lens system that cancels extra tilting of the reflected light off a silicon nitride membrane mechanical resonator caused by laser-pointing-noise-induced optical torques. We achieve a readout noise floor two orders of magnitude lower than the SQL, corresponding to an effective optomechanical cooperativity of 100 without the need for an optical cavity. As the state-of-the-art ultralow dissipation optomechanical systems relevant for quantum sensing are rapidly approaching the level where quantum noise dominates, simple and widely applicable back action evading protocols will be crucial for pushing beyond quantum limits.

中文翻译：

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光学杠杆检测中的后向动作规避

光学杠杆是一种有着数百年历史且广泛使用的检测技术，其应用范围从消费产品和工业传感器到科学研究中使用的精密力显微镜。然而，尽管历史悠久，其量子极限仍有待探索。一般来说，任何精密光学测量都会伴随着光学力对被测物体产生的干扰（称为反作用），从而导致标准量子极限（SQL）。在这里，我们给出了如何在光学杠杆检测中避免这种反向作用的简单射线光学描述。我们进行了原理验证实验，通过开发一种透镜系统来消除由激光指向噪声引起的氮化硅膜机械谐振器反射光的额外倾斜，展示了经典机制中的反作用规避机制。光学扭矩。我们实现了比 SQL 低两个数量级的读出本底噪声，相当于无需光学腔即可实现 100 的有效光机协同性。随着与量子传感相关的最先进的超低耗散光机械系统迅速接近量子噪声占主导地位的水平，简单且广泛适用的反作用规避协议对于突破量子极限至关重要。