Quantum cooling and squeezing of a levitating nanosphere via time-continuous measurements

TL;DR

This paper demonstrates that continuous measurement and feedback can cool and squeeze a levitating nanosphere's quantum state, achieving non-classical steady states with low phonon numbers using current experimental setups.

Contribution

It introduces a method combining sideband cooling, continuous measurement, and feedback to stabilize and produce non-classical states of a levitating nanosphere.

Findings

Continuous measurement enhances non-classicality of the steady state.

Stable non-classical states with phonon number around 0.5 are achievable.

The approach is feasible with current experimental parameters.

Abstract

With the purpose of controlling the steady state of a dielectric nanosphere levitated within an optical cavity, we study its conditional dynamics under simultaneous sideband cooling and additional time-continuous measurement of either the output cavity mode or the nanosphere's position. We find that the average phonon number, purity and quantum squeezing of the steady-states can all be made more non-classical through the addition of time-continuous measurement. We predict that the continuous monitoring of the system, together with Markovian feedback, allows one to stabilize the dynamics for any value of the laser frequency driving the cavity. By considering state-of-the-art values of the experimental parameters, we prove that one can in principle obtain a non-classical (squeezed) steady-state with an average phonon number $n_{\sf ph}\approx 0.5$.