Librational Feedback Cooling

Abstract

Librational motion, whereby a rigid body undergoes angular oscillation around a preferred direction, can be observed in optically trapped, silica microspheres. We demonstrate the cooling of one librational degree of freedom for $\sim 5\mu$m diameter spheres that have been induced to rotate with an external electric field coupled to their electric dipole moment. Cooling is accomplished by adding a phase modulation to the rotating field. The degree of cooling is quantified by applying a $\pi /2$ shift to the phase of the electric field and fitting the resulting exponential decay of the librational motion to obtain a damping time, as well as estimating a mode temperature from the observed libration in equilibrium. The result is an important step in the study of the dynamics of trapped microspheres, crucial to cooling the mechanical motion to its ground state, as well as providing insights regarding the charge mobility in the material at microscopic scales.

8 pages, 7 figures

References in corpus (5)

• Motional Quantum Ground State of a Levitated Nanoparticle from Room Temperature
• Search for Millicharged Particles Using Optically Levitated Microspheres
• Cold Damping of an Optically Levitated Nanoparticle to micro-Kelvin Temperatures
• Optimal Feedback Cooling of a Charged Levitated Nanoparticle with Adaptive Control
• Absolute pressure and gas species identification with an optically levitated rotor