Quantum Delocalization of a Levitated Nanoparticle

TL;DR

This paper demonstrates the creation of a quantum delocalized state in a levitated nanosphere, surpassing the zero-point motion, advancing macroscopic quantum experiments and quantum sensing capabilities.

Contribution

It reports the first preparation of a delocalized quantum state of a levitated solid-state nanoparticle with coherence length exceeding zero-point motion.

Findings

Achieved over threefold increase in coherence length of a levitated nanosphere

Successfully cooled the nanosphere to its quantum ground state

Demonstrated control of delocalization via modulation of confinement stiffness

Abstract

Every massive particle behaves like a wave, according to quantum physics. Yet, this characteristic wave nature has only been observed in double-slit experiments with microscopic systems, such as atoms and molecules. The key aspect is that the wavefunction describing the motion of these systems extends coherently over a distance comparable to the slit separation, much larger than the size of the system itself. Preparing these states of more massive and complex objects remains an outstanding challenge. While the motion of solid-state oscillators can now be controlled at the level of single quanta, their coherence length remains comparable to the zero-point motion, limited to subatomic distances. Here, we prepare a delocalized state of a levitating solid-state nanosphere with coherence length exceeding the zero-point motion. We first cool its motion to the ground state. Then, by modulating the stiffness of the confinement potential, we achieve more than a threefold increment of the initial coherence length with minimal added noise. Optical levitation gives us the necessary control over the confinement that other mechanical platforms lack. Our work is a stepping stone towards the generation of delocalization scales comparable to the object size, a crucial regime for macroscopic quantum experiments, and towards quantum-enhanced force sensing with levitated particles.