Investigating and Controlling the Libration and Rotation Dynamics of Nanoparticles in an Optomechanical System

TL;DR

This paper explores how monitoring scattered light reveals the transition dynamics between libration and rotation of nanoparticles in optomechanical systems, enabling precise control and insights into quantum effects.

Contribution

It demonstrates real-time observation of nanoparticle libration-rotation transitions via scattered light and links these to optical torque balances, advancing nanoparticle control in quantum optomechanics.

Findings

Real-time monitoring of libration/rotation transitions.

Identification of absorption as main contributor to constant torque.

Potential for weak torque sensing and quantum state studies.

Abstract

In optomechanical systems, the libration and rotation of nanoparticles offer profound insights for ultrasensitive torque measurement and macroscopic quantum superpositions. Achievements include transitioning libration to rotation up to 6 GHz and cooling libration to millikelvin temperatures. It is undoubted that the libration and rotation are respectively driven by restoring and constant optical torques. The transition mechanisms between these two states, however, demand further exploration. In this perspective, it is demonstrated in this manuscript that monitoring lateral-scattered light allows real-time observation of libration/rotation transitions and associated hysteresis as ellipticities of trapping laser fields vary. By calculating optical torques and solving the Langevin equation, transitions are linked to the balance between anisotropic-polarization-induced sinusoidal optical torques and constant ones, with absorption identified as the main contributor to constant torques. These findings enable direct weak torque sensing and precise nanoparticle control in rotational degrees, paving the way for studying quantum effects like nonadiabatic phase shifts and macroscopic quantum superpositions, thereby enriching quantum optomechanics research.