Experimental Investigation of the Quantum Measurement Process Using Electrons in Superfluid Helium

We report on mobility measurements of electron bubbles in superfluid helium-4. Electrons are introduced into the liquid from a plasma discharge in the vapor. For electrons with energy only a small amount above the minimum energy needed to enter the liquid, the wave function is partially transmitted into the liquid. We investigate the possibility that this partial transmission results in the formation of stable electron bubbles each of which contains only a fraction of the complete electron wave function. By measuring the mobility of these bubbles we can estimate their size. Our simulation of the mobility of these bubbles is consistent with the experimental data, and supports the idea that the interaction of the electron with the liquid helium does not result in a measurement that immediately determines that an electron is, or is not, in the bubble. Other possible explanations and their difficulties are also discussed in the paper.