Microspheres with atomic-scale tolerances generate hyper-degeneracy

Highly symmetrical objects are important to a manifold of applications such as precise measurements and sensing. However, creating a perfect sphere proves to be experimentally extremely difficult, as gravity and the support deform the sphere from its perfect shape. In this work, we optically levitate a micro oil droplet and activate it as whispering gallery mode optical resonator. Our contactless resonator displays a sphericity of less than one Angstrom for a 10 µm radius droplet and is therefore one of the roundest objects there is. Additionally, we demonstrate an unprecedented resonance enhancement defined by “optical quality” over “mode volume” and lastly, benefitting from the high sphericity, we lift degeneracies of order higher than 200.