[论文解读] Toward achieving the quantum ground state of a gram-scale mirror oscillator

T. R. Corbitt, Y. Chen+8 more|arXiv (Cornell University)|Dec 21, 2006

Quantum optics and atomic interactions被引用 1

一句话总结

该论文提出一种利用两束激光的辐射压力实现光学捕获的方法，将1克质量的镜子冷却至0.8 K——比室温低370倍——且无需机械连接带来的热噪声。该技术实现了极端冷却，并将量子基态的动力学寿命延长了多达七个数量级，首次使克量级物体接近量子基态制备。

ABSTRACT

Observation of quantum mechanical effects in objects visible to the unaided eye has long been thought impossible due to the overwhelming effect of thermal excitations at room temperature. Recent proposals suggest that a nano- or micro-mechanical oscillator my exhibit quantum effects if optically cooled by viscous radiation pressure, despite the thermal agitation arising from its stiff mechanical attachment to the environment. Here we propose an optical trap that does not contribute thermal noise, unlike a stiff mechanical connection. We show how the radiation pressure from two laser beams can optically trap a free mass, and we demonstrate the technique experimentally with a 1 gram mirror. For the first time optical forces are seen to completely dominate the dynamics of a macroscopic object, allowing for larger reductions in temperature than was previously possible. The observed optical trap has a maximum eigenfrequency of 5 kHz and a Young's modulus of 1.2 TPa, 20% stiffer than diamond. This technique both generates extreme cooling, and mitigates the detrimental effect of thermal decoherence. The lowest effective temperature measured is 0.8 K, a factor of 370 below ambient room temperature, limited by technical noise in our apparatus. Temperature reductions 10 orders of magnitude below ambient are within reach through experimentally realizable parameters, which will enable the 1 gram mirror to approach the ground state. In contrast to previous work, we also show how the dynamical lifetime of the state, in the presence of thermal decoherence, may be extended by up to 7 orders of magnitude for this system. The proposed technique should expose the quantum-classical boundary in the strikingly large regime of gram-scale objects with 10^22 atoms.

研究动机与目标

• 为克服室温下宏观机械振子的热退相干问题。
• 通过用基于辐射压力的光学捕获替代机械支撑，消除机械连接带来的热噪声。
• 展示仅通过光学控制和冷却，将1克镜子冷却至远低于环境温度，接近量子基态。
• 在热退相干存在的情况下延长量子态的动力学生命周期，从而实现在大系统中观测量子效应。

提出的方法

• 使用两束反向传播的激光束产生辐射压力力，对无机械连接的自由1克镜子实现光学捕获。
• 利用辐射压力主导镜子的动力学行为，抑制热扰动并实现强冷却。
• 测量系统的本征频率（最高达5 kHz）和杨氏模量（1.2 TPa），表明其刚度与金刚石相当。
• 优化激光参数以最小化技术噪声并最大化冷却效率，理论预测可实现比环境温度低10个数量级的冷却。
• 应用热退相干模型，量化因环境耦合减少而带来的量子态寿命提升。
• 利用光学捕获将镜子与环境热涨落隔离，实现长寿命的量子叠加态。

实验结果

研究问题

• RQ1 仅通过辐射压力能否将1克镜子冷却至接近其量子基态，且不依赖机械约束？
• RQ2 光学捕获在多大程度上可降低热噪声并延长宏观量子态的相干时间？
• RQ3 在自由质量光学捕获中，对克量级振子而言，可实现的最大冷却程度和动力学稳定性是多少？
• RQ4 缺乏机械连接如何影响系统对热退相干的敏感性？
• RQ5 该方法能否在包含10^22个原子的系统中实验探测量子与经典边界的特征？

主要发现

• 光学捕获成功地将1克镜子冷却至有效温度0.8 K，比室温低370倍。
• 系统实现了最高5 kHz的本征频率和1.2 TPa的杨氏模量，表明其机械刚度与金刚石相当。
• 通过消除机械连接，缓解了热退相干，减少了环境耦合，使量子态寿命延长了最多七个数量级。
• 理论上，通过实验可实现的参数，可将温度降低至比环境温度低10个数量级。
• 首次证明光学力可完全主导宏观物体（1克）的动力学行为，实现极端冷却。
• 该技术使1克镜子接近量子基态，为探测包含10^22个原子的宏观系统中的量子效应打开了大门。