CAREER: Quantum Spin-Optomechanics of Optically Levitated Nanodiamonds

非常小的粒子可以以与常识相反的方式运动。例如，一个电子（构成原子的粒子之一）可以同时出现在多个位置，并且可以穿过屏障——这是经典物理定律所禁止的。解释这些小粒子反直觉行为的理论是“量子力学”。这个CAREER项目将研究使量子力学在更大、更宏观的系统中显现的可能性。具体来说，该项目将研究如何将电子的自旋与纳米粒子（包含数百万个原子）的运动耦合起来。纳米粒子将在真空中由激光束悬浮，以避免环境的扰动。该系统应作为一个非常敏感的力检测器，具有许多应用。它可能使其他实验能够研究广义相对论和量子力学之间的冲突，这是物理学中一个长期存在的问题。该研究将与几个相关的教育活动相结合，包括直接培训参与研究的研究生和本科生，以及为初高中教师和学生举办红外光探究讲习班。红外光是人眼不可见的，但在全球变暖和光纤通信中起着至关重要的作用。在本研究中，将利用红外光使纳米粒子在真空中悬浮。教师们在车间里用红外光进行动手实验后，就可以把他们的仪器带到教室里使用了。在更多的技术细节上，该研究项目将开发一种结合了捕获原子和传统光力学系统的优点来研究宏观量子力学的系统：一种具有内置氮空位（NV）中心的光学悬浮纳米金刚石。在某些方面，这个系统可以被认为是一个质量非常大的“人造原子”。NV中心的电子自旋可以随磁场梯度耦合到纳米金刚石的运动。这种耦合可以用来创建纳米金刚石的大量子空间叠加态，这将导致纳米粒子物质波干涉仪的发展，用于在未探索的参数体系中进行量子力学的基本测试。这个CAREER项目的主要重点将是实验研究NV电子自旋与光学悬浮纳米金刚石的质心运动和旋转之间的耦合。通过主动反馈冷却将悬浮纳米金刚石的运动冷却到接近量子基态。NV电子自旋将被用来感知和操纵纳米金刚石的运动。它还将用于测量悬浮纳米金刚石内部温度对量子相干时间的影响。

Very small particles can behave in ways that are contrary to common sense. For example, an electron (one of the particles that make up atoms) can be at multiple locations at the same time and can tunnel through a barrier--something forbidden by the classical laws of physics. The theory that explains these counterintuitive behaviors of small particles is "quantum mechanics". This CAREER project will investigate the possibility of making quantum mechanics appear manifest in larger, more macroscopic, systems. In specific, the project will investigate how to couple the spin of an electron to the motion of a nanoparticle (containing millions of atoms). The nanoparticle will be levitated by a laser beam in vacuum to avoid perturbations from the environment. This system should serve as a very sensitive force detector with many applications. It may enable other experiments to study the conflict between general relativity and quantum mechanics, a longstanding problem in physics. The research will be integrated with several related educational activities, including direct training of graduate and undergraduate students participating in the research, and conducting inquiry workshops about infrared light for middle and high school teachers and students. Infrared light is not visible to human eyes, but plays a crucial role in global warming and fiber-optic communication. In the present work, infrared light will be used to levitate nanoparticles in vacuum. After doing hands-on experiments with infrared light in the workshop, teachers will be able to take their apparatus for use in their classrooms.In more technical detail, this research project will develop a system that combines the advantages of both trapped atoms and conventional optomechanical systems for studying macroscopic quantum mechanics: an optically levitated nanodiamond with a built-in nitrogen-vacancy (NV) center. In some ways, this system can be considered to be an "artificial atom" with a very large mass. The electron spin of the NV center can be coupled to the motion of the nanodiamond with a magnetic field gradient. This coupling can be used to create large quantum spatial superposition states of the nanodiamond, which will lead to the development of a nanoparticle matter-wave interferometer for fundamental tests of quantum mechanics in unexplored parameter regimes. The main focus of this CAREER project will be to experimentally study the coupling between an NV electron spin and both the center-of-mass motion and the rotation of an optically levitated nanodiamond. The motion of the levitated nanodiamond will be cooled to near quantum ground state by active feedback cooling. The NV electron spin will be used to sense and manipulate the motion of the nanodiamond. It will also be used to measure the internal temperature of the levitated nanodiamond which affects the quantum coherence time.