Observations of the Motion of Single Electrons in Liquid Helium

We have developed an apparatus which can be used to monitor the motion of individual electrons in liquid helium. A sound wave is used to explode an electron bubble for a fraction of a microsecond. While the bubble is expanded, it is illuminated by light from a flash lamp. We describe the details of the experiment and show results obtained. In some cases, an electron is seen to follow a snakelike path. Our tentative explanation is that the electron is sliding along a quantized vortex line. If this interpretation is correct, the recorded track of the electron provides an image of the path of the vortex.