Interaction Between an Optically Levitated Nanoparticle and Its Thermal Image: Internal Thermometry via Displacement Sensing

TL;DR

This paper proposes a theoretical method to measure a nanoparticle's internal temperature by sensing its displacement caused by thermal image interactions near a surface, advancing internal thermometry techniques.

Contribution

It introduces a novel approach to internal thermometry of levitated nanoparticles using displacement sensing of dipole-dipole interactions with thermal images.

Findings

The dipole-dipole interaction force exceeds thermal gradient forces.

The force depends strongly on the nanoparticle's internal temperature.

Feasibility of using displacement sensing as an internal thermometer is demonstrated.

Abstract

We propose and theoretically analyze an experiment where displacement sensing of an optically levitated nanoparticle in front of a surface can be used to measure the induced dipole-dipole interaction between the nanoparticle and its thermal image. This is achieved by using a surface that is transparent to the trapping light but reflective to infrared radiation, with a reflectivity that can be time modulated. This dipole-dipole interaction relies on the thermal radiation emitted by a silica nanoparticle having sufficient temporal coherence to correlate the reflected radiation with the thermal fluctuations of the dipole. The resulting force is orders of magnitude stronger than the thermal gradient force and it strongly depends on the internal temperature of the nanoparticle for a particle-to-surface distance greater than two micrometers. We argue that it is experimentally feasible to use displacement sensing of a levitated nanoparticle in front of a surface as an internal thermometer. Experimental access to the internal physics of a levitated nanoparticle in vacuum is crucial to understand the limitations that decoherence poses to current efforts devoted to prepare a nanoparticle in a macroscopic quantum superposition state.