QUANTUM INTERFERENCE IN ELECTRON COLLISION

The indistinguishability of identical quantum particles can lead to qu antum interferences that profoundly affect their scattering(1,2). If t wo particles collide and scatter, the process that results in the dete ction of the first particle in one direction and the second particle i n another direction interferes quantum mechanically with the physicall y indistinguishable process where the roles of the particles are rever sed. For bosons such as photons, a constructive interference between p robability amplitudes can enhance the probability, relative to classic al expectations, that both are detected in the same direction-this is known as 'bunching'. But for fermions such as electrons, a destructive interference should suppress this probability ('anti-bunching'); this interference is the origin of the Pauli exclusion principle, which st ates that two electrons can never occupy the same state. Although two- particle interferences have been shown for colliding photons(3,4), no similar demonstration for electrons exists(2,5,6). Here we report the realization of this destructive quantum interference in the collision of electrons at a beam splitter. In our experiments, the quantum inter ference responsible for the Pauli exclusion principle is manifest as t he suppression in electron current noise after collision.