Quantum control of a nanoparticle optically levitated in cryogenic free space

TL;DR

This paper demonstrates quantum control of a levitated nanoparticle in cryogenic free space, achieving ground-state cooling and highlighting its potential for macroscopic quantum mechanics experiments.

Contribution

It introduces a novel platform for quantum control of a levitated nanoparticle without an optical resonator, enabling advanced macroscopic quantum experiments.

Findings

Achieved cooling to 0.65 motional quanta

Demonstrated measurement-based quantum control

Suppressed thermal effects in cryogenic free space

Abstract

Tests of quantum mechanics on a macroscopic scale require extreme control over mechanical motion and its decoherence. Quantum control of mechanical motion has been achieved by engineering the radiation-pressure coupling between a micromechanical oscillator and the electromagnetic field in a resonator. Furthermore, measurement-based feedback control relying on cavity-enhanced detection schemes has been used to cool micromechanical oscillators to their quantum ground states. In contrast to mechanically tethered systems, optically levitated nanoparticles are particularly promising candidates for matter-wave experiments with massive objects, since their trapping potential is fully controllable. In this work, we optically levitate a femto-gram dielectric particle in cryogenic free space, which suppresses thermal effects sufficiently to make the measurement backaction the dominant decoherence mechanism. With an efficient quantum measurement, we exert quantum control over the dynamics of the particle. We cool its center-of-mass motion by measurement-based feedback to an average occupancy of 0.65 motional quanta, corresponding to a state purity of 43%. The absence of an optical resonator and its bandwidth limitations holds promise to transfer the full quantum control available for electromagnetic fields to a mechanical system. Together with the fact that the optical trapping potential is highly controllable, our experimental platform offers a route to investigating quantum mechanics at macroscopic scales.