Optically levitated multiple nanoparticles have emerged as a platform for studying complex fundamental physics such as non-equilibrium phenomena, quantum entanglement, and light–matter interaction, which could be applied for sensing weak forces and torques with high sensitivity and accuracy. An optical trapping landscape of increased complexity is needed to engineer the interaction between levitated particles beyond the single harmonic trap. However, existing platforms based on spatial light modulators for studying interactions between levitated particles suffered from low efficiency, instability at focal points, the complexity of optical systems, and the scalability for sensing applications. Here, we experimentally demonstrated that a metasurface which forms two diffraction-limited focal points with a high numerical aperture (∼0.9) and high efficiency (31 %) can generate tunable optical potential wells without any intensity fluctuations. A bistable potential and double potential wells were observed in the experiment by varying the focal points’ distance, and two nanoparticles were levitated in double potential wells for hours, which could be used for investigating the levitated particles’ nonlinear dynamics, thermal dynamics and optical binding. This would pave the way for scaling the number of levitated optomechanical devices or realizing paralleled levitated sensors.

中文翻译：

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基于单层超表面的可调谐片上光阱悬浮粒子

光悬浮多个纳米颗粒已成为研究非平衡现象、量子纠缠和光与物质相互作用等复杂基础物理的平台，可用于高灵敏度和高精度地传感弱力和扭矩。需要增加复杂性的光学捕获景观来设计单谐波陷阱之外的悬浮粒子之间的相互作用。然而，现有的基于空间光调制器的用于研究悬浮粒子之间相互作用的平台存在效率低、焦点不稳定、光学系统复杂以及传感应用的可扩展性等问题。在这里，我们通过实验证明，形成两个具有高数值孔径（∼0.9）和高效率（31％）的衍射极限焦点的超表面可以产生可调谐光学势阱，而不会产生任何强度波动。实验中通过改变焦点距离观察到双稳态势和双势井，并将两个纳米粒子悬浮在双势井中数小时，可用于研究悬浮粒子的非线性动力学、热动力学和光学结合。这将为扩大悬浮光机械设备的数量或实现并行悬浮传感器铺平道路。