CAREER: Quantum Spin-Optomechanics of Optically Levitated Nanodiamonds

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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.