  The electron bubble in superfluid helium has two degrees of freedom that may
offer exceptionally low dissipation: the electron's spin and the bubble's
motion. If these degrees of freedom can be read out and controlled with
sufficient sensitivity, they would provide a novel platform for realizing a
range of quantum technologies and for exploring open questions in the physics
of superfluid helium. Here we propose a practical scheme for accomplishing this
by trapping an electron bubble inside a superfluid-filled opto-acoustic cavity.
