We discuss annular confinement for electrons on liquid helium surface induced by a tubular electrode submerged beneath the surface. For shallow layer above tube resulting potential has minimum off axis of tube. The symmetry transitions in ground-state driven external magnetic field can be resolved microwave spectroscopy provided that radii first and second Rydberg subbands vertical quantization...

We report on the observation of a new type of electron bubble in superfluid helium-4. This object appears to be larger than the normal electron bubble and is associated with the presence of quantized vortices in the liquid.