Science http://doi.org/kg8 (2013)

Interference is one of the hallmarks of a wave. The effect is even evident at the quantum level, when waves start to display properties more usually associated with particles. Erwann Bocquillon and colleagues now demonstrate this concept in reverse: individual particles acting like waves and interfering.

A single wavepacket can leave a beam splitter by one of two exits with equal probability. When two indistinguishable wavepackets meet in the beam splitter, they interfere and their exit directions become inherently linked. Photons, for example, both leave the same way. Electrons always take opposite exits. This is the Hong–Ou–Mandel effect.

Bocquillon and team created two quantum-dot single-electron sources. The individual electrons from each source were synchronized so that they simultaneously arrived at an electronic beam splitter. The researchers demonstrated a correlation in the electrons' exit paths by measuring how the low-frequency fluctuations of the electrical current in the outputs were related to the fluctuations of the number of transmitted particles. This demonstration of interference showed that the two electrons were indistinguishable even though they came from different sources.