Low-energy scattering of ultracold atoms by a dielectric nanosphere

TL;DR

This paper provides a theoretical analysis of low-energy ultracold atom scattering by a dielectric nanosphere, highlighting quantum effects like diffraction and s-wave reflection at microkelvin and nanokelvin energies.

Contribution

It introduces a detailed quantum-classical comparison of atom-nanosphere scattering, emphasizing the emergence of quantum effects at ultracold temperatures and their dependence on nanosphere size.

Findings

Quantum differential cross section deviates from classical at microkelvin energies due to diffraction.

Quantum effects like s-wave reflection appear below nanokelvin energies.

Scattering properties depend on the nanosphere radius.

Abstract

We theoretically study the low-energy scattering of ultracold atoms by a dielectric nanosphere of silica glass levitated in a vacuum. The atom and dielectric surface interact via dispersion force of which strength sensitively depends on the polarizability, dielectric function, and geometry. For cesium and rubidium atoms, respectively, we compute the atom-surface interaction strength, and characterize the stationary scattering states by taking adsorption of the atoms onto the surface into account. As the energy of the incoming atoms is lowered, we find that differences between quantum and classical scatterings emerge in two steps. First, the quantum-mechanical differential cross section of the elastic scattering starts to deviate from the classical one at an energy scale comparable to a few microkelvin in units of temperature due to the de Broglie matter-wave diffraction. Second, the differences are found in the cross sections in a regime lower than a few nanokelvin, where the classically forbidden reflection occurs associated with the $s$-wave scattering, and the discrete nature of angular momentum. We also study the dependencies of quantum and classical scattering properties on the radius of the nanosphere. This paper paves the way to identify the quantum regime and to understand the physical origin of quantum effects in the collisions between a nanoparticle and environmental gas over various temperatures.