Controlling mode orientations and frequencies in levitated cavity optomechanics

TL;DR

This paper demonstrates that by adjusting the coherent-scattering setup in levitated cavity optomechanics, it is possible to cancel optical spring effects and mode hybridisation, enabling control of unperturbed mechanical modes for quantum applications.

Contribution

The study introduces a method to cancel optical spring shifts and mode hybridisation in levitated optomechanics using coherent scattering, allowing independent control of mechanical modes.

Findings

Achieved cancellation of optical spring effects at an optimal point.

Demonstrated suppression of mode hybridisation in the x-y plane.

Measured uncorrelated spectra indicating effective mode control.

Abstract

Cavity optomechanics offers quantum cooling, quantum control and measurement of small mechanical oscillators. However the optical backactions that underpin quantum control can significantly disturb the oscillator modes: mechanical frequencies are shifted by the optical spring effect and light-matter hybridisation in strong coupling regimes; mechanical modes hybridise with each other via the cavity mode. This is even more pertinent in the field of levitated optomechanics, where optical trapping fully determines the mechanical modes and their frequencies. Here, using the coherent-scattering (CS) set-up that allowed quantum ground state cooling of a levitated nanoparticle, we show that -- when trapping away from a node of the cavity standing wave -- the CS field opposes optical spring shifts and mechanical mode hybridisation. At an optimal cancellation point, independent of most experimental parameters, we demonstrate experimentally that it is possible to strongly cavity cool and control the {\em unperturbed} modes. Suppression of the cavity-induced mode hybridisation in the $x-y$ plane is quantified by measuring the $S_{xy}(\omega)$ correlation spectra which are seen to always be anti-correlated except at the cancellation point where they become uncorrelated. The findings have implications for directional force sensing using CS set-ups.