State Expansion of a Levitated Nanoparticle in a Dark Harmonic Potential

TL;DR

This paper demonstrates a method to expand and recontract the quantum state of a levitated nanoparticle using a hybrid optical and Paul trap system, enabling large-scale state manipulation without measurement backaction.

Contribution

It introduces a novel hybrid trapping scheme that allows significant state expansion of a nanoparticle's thermal state without recoil-induced backaction, advancing quantum state control.

Findings

Achieved a 25-fold expansion in state standard deviation.

Expanded thermal state of a nanoparticle from 155 mK.

Method avoids measurement backaction, suitable for quantum experiments.

Abstract

Levitated nanoparticles in vacuum are prime candidates for generating macroscopic quantum superposition states of massive objects. Most protocols for preparing these states necessitate coherent expansion beyond the scale of the zero-point motion to produce sufficiently delocalized and pure phase-space distributions. Here, we spatially expand and subsequently recontract the thermal state of a levitated nanoparticle by modifying the stiffness of the trap holding the particle. We achieve state-expansion factors of 25 in standard deviation for a particle initially feedback-cooled to a center-of-mass thermal state of \SI{155}{\milli\kelvin}. Our method relies on a hybrid scheme combining an optical trap, for cooling and measuring the particle's motion, with a Paul trap for expanding its state. Consequently, state expansion occurs devoid of measurement backaction from photon recoil, making this approach suitable for coherent wavefunction expansion in future experiments.