Thai M. Hoang

Torsional Optomechanics of a Levitated Nonspherical Nanoparticle

An optically levitated nanoparticle in vacuum is a paradigm optomechanical system for sensing and studying macroscopic quantum mechanics. While its center-of-mass motion has been investigated intensively, its torsional vibration has only been studied theoretically in limited cases. Here we report the first experimental observation of the torsional vibration of an optically levitated nonspherical nanoparticle in vacuum. We achieve this by utilizing the coupling between the spin angular momentum of photons and the torsional vibration of a nonspherical nanoparticle whose polarizability is a tensor. The torsional vibration frequency can be 1 order of magnitude higher than its center-of-mass motion frequency, which is promising for ground state cooling. We propose a simple yet novel scheme to achieve ground state cooling of its torsional vibration with a linearly polarized Gaussian cavity mode. A levitated nonspherical nanoparticle in vacuum will also be an ultrasensitive nanoscale torsion balance with a torque detection sensitivity on the order of 10^{-29}u2009u2009Nu2009m/sqrt[Hz] under realistic conditions.

Electron spin control of optically levitated nanodiamonds in vacuum

We optically levitated a nanodiamond in partial vacuum and demonstrated electron spin control of its built-in nitrogen-vacancy centers. We observed that the strength of electron spin resonance is enhanced when the air pressure is reduced.

Proposal for quantum many-body simulation and torsional matter-wave interferometry with a levitated nanodiamond

Hybrid spin-mechanical systems have great potentials in sensing, macroscopic quantum mechanics, and quantum information science. In order to induce strong coupling between an electron spin and the center-of-mass motion of a mechanical oscillator, a large magnetic gradient is usually required, which is difficult to achieve. Here we show that strong coupling between the electron spin of a nitrogen-vacancy (NV) center and the torsional vibration of an optically levitated nanodiamond can be achieved in a uniform magnetic field. Thanks to the uniform magnetic field, multiple spins can strongly couple to the torsional vibration at the same time. We propose to utilize this new coupling mechanism to realize the Lipkin-Meshkov-Glick (LMG) model by an ensemble of NV centers in a levitated nanodiamond. The quantum phase transition in the LMG model and finite number effects can be observed with this system. We also propose to generate torsional superposition states and realize torsional matter-wave interferometry with spin-torsional coupling.

Torsional optomechanics and quantum simulation with a levitated nanodiamond

We report the observation of the torsional vibration of an optically levitated nanodiamond in vacuum. We propose a scheme to achieve torsional ground state cooling, and utilize the electron spin-torsional coupling to do quantum simulation.