Optically Levitated Nanodumbbell Torsion Balance and GHz Nanomechanical Rotor

TL;DR

This paper demonstrates a novel optically levitated nanodumbbell torsion balance with high torque sensitivity and ultrafast GHz rotation, opening new avenues for quantum sensing, fundamental physics, and material studies.

Contribution

It introduces a new levitated nanodumbbell torsion balance with unprecedented torque sensitivity and achieves the fastest nanomechanical rotation beyond 1 GHz.

Findings

Torque detection sensitivity exceeds current torsion balances by several orders.

Achieved nanodumbbell rotation beyond 1 GHz, the fastest to date.

Potential to observe Casimir torque and probe quantum gravity effects.

Abstract

Levitated optomechanics has great potentials in precision measurements, thermodynamics, macroscopic quantum mechanics and quantum sensing. Here we synthesize and optically levitate silica nanodumbbells in high vacuum. With a linearly polarized laser, we observe the torsional vibration of an optically levitated nanodumbbell in vacuum. The linearly-polarized optical tweezer provides a restoring torque to confine the orientation of the nanodumbbell, in analog to the torsion wire which provides restoring torque for suspended lead spheres in the Cavendish torsion balance. Our calculation shows its torque detection sensitivity can exceed that of the current state-of-the-art torsion balance by several orders. The levitated nanodumbbell torsion balance provides rare opportunities to observe the Casimir torque and probe the quantum nature of gravity as proposed recently. With a circularly-polarized laser, we drive a 170-nm-diameter nanodumbbell to rotate beyond 1~GHz, which is the fastest nanomechanical rotor realized to date. Our calculations show that smaller silica nanodumbbells can sustain rotation frequency beyond 10 GHz. Such ultrafast rotation may be used to study material properties and probe vacuum friction.