# Bistability and squeezing of the librational mode of an optically trapped nanoparticle

## TL;DR

This paper explores the nonlinear dynamics, bistability, and quantum squeezing of the librational mode in a levitated nanoparticle, revealing dependencies on particle properties and potential applications in precise measurements.

## Contribution

It introduces a detailed analysis of the nonlinear librational potential up to fourth order, highlighting its dependence on nanoparticle size and material, and investigates bistability and squeezing phenomena.

## Key findings

- Bistability occurs with red-detuned driving frequency.
- Squeezing of librational mode variance is achieved in blue-detuned region.
- Nonlinear coefficient depends on nanoparticle size and material, not trap shape.

## Abstract

We systematically investigate the bistable behavior and squeezing property of the librational mode of a levitated nonspherical nanoparticle trapped by laser beams. By expanding the librational potential to the forth order of the librational angle $\theta$, we find that the nonlinear coefficient of this mode is dependent only on the size and material of nanoparticle, but independent of trapping potential shape. The bistability and hysteresis are displayed when the driving frequency is red-detuned to the librational mode. In the blue-detuned region, we have studied squeezing of the variance of librational mode in detail, which has potential application for measurement of angle and angular momentum.