The Double Slit Experiment for Electrons

Abstract

Together with the double slit experiment for photons the corresponding experiment for electrons represents one of the most celebrated and famous experiments in physics. Its fame is due more to the conceptual problems it creates rather than its contribution to understanding quantum physics. The observation of wavelike diffraction of electrons and their definite particlelike behavior in other circumstances has remained a conceptual mystery in quantum physics until this day. The basic experimental setup shown in Fig. 8.1 is simple enough. A stream of focused electrons from a hot cathode impinges on a plate with two narrow slits separated a small distance apart. The electrons transmitted through the slits are observed to form a typical diffraction pattern on the screen behind the slit plate. If the intensity of the electron source is reduced to the point when only one electron at a time is reaching the screen, it produces a pointlike spot located somewhere on the screen, not necessarily just below the slits. This behavior is certainly in accord with classical concepts of the electron as a particle, with the electron passing through one of the two slits. In the process it is deflected by some angle and finally hitting the screen at some localized point. The deflection has no classical explanation. But there are worse things to come.

She went on, “Would you tell me please which way I ought to go from here?” “That depends a good deal on where you want to get to,” said the Cat “I don’t much care where—” said Alice. “Then it doesn’t matter which way you go,” said the Cat “—as long as I get somewhere,” Alice added as an explanation. “Oh, you are sure to do that,” said the Cat, “if you walk long enough.”

Lewis Carroll Alice in Wonderland