# Auxiliary-cavity-assisted ground-state cooling of optically levitated nanosphere in the unresolved-sideband regime

## TL;DR

This paper proposes a method to achieve ground-state cooling of an optically levitated nanosphere in the unresolved-sideband regime by introducing a coupled high-quality-factor cavity, leveraging quantum interference to enhance cooling efficiency.

## Contribution

It introduces a coupled cavity scheme that enables ground-state cooling in the unresolved-sideband regime, even with weak optomechanical coupling, by exploiting quantum interference effects.

## Key findings

- Ground-state cooling is achievable in unresolved-sideband regime with coupled cavity.
- Quantum interference modifies optical force spectral density and breaks heating-cooling symmetry.
- Coupled cavity enhances system stability and effective resolved regime conditions.

## Abstract

We theoretically analyse the ground-state cooling of optically levitated nanosphere in unresolved- sideband regime by introducing a coupled high-quality-factor cavity. On account of the quantum interference stemming from the presence of the coupled cavity, the spectral density of the optical force exerting on the nanosphere gets changed and then the symmetry between the heating and the cooling processes is broken. Through adjusting the detuning of strong-dissipative cavity mode, one obtains an enhanced net cooling rate for the nanosphere. It is illustrated that the ground state cooling can be realized in the unresolved sideband regime even if the effective optomechanical coupling is weaker than the frequency of the nanosphere, which can be understood by the picture that the effective interplay of the nanosphere and the auxiliary cavity mode brings the system back to an effective resolved regime. Besides, the coupled cavity refines the dynamical stability of the system.