A water droplet as a toy atom

Paper in proceeding, 2022

Common atomic physics courses jump from the square and harmonic well potentials straight to the hydrogen atom. However, there is a missing link in between, the spherical well potential. Although it is included in some textbooks, the lack of an experimental backing means the problem quickly becomes mathematically complex. Here we have built an optical toy atom using the scattering of an optically levitated, evaporating water droplet. We find a greatly simplified Mie scattering spectrum composed of a series of evolving Fano resonances organized in a set of combs. The whole spectrum can be intuitively explained through an analogy to a quantum spherical well potential. This produces a model of an atom including ground and excited states, quantized angular momentum, and tunneling.