Physicists from Heidelberg Unversity, and colleagues from Technische Universität (München and Wein), have extended a thought experiment by Einstein and managed to blur the distinction between a particle and its mirror image by creating quantum superpositions.

The physicists experimentally produced motional coherence by a single spontaneous emission event close to a mirror surface. By placing atoms close to the mirror’s surface, they demonstrated that there are two possible paths for any photon traveling to an observer: one emitted directly in the direction of the observer, and a second traveling in the opposite direction and reflected in the mirror.

They showed that if there is no way of distinguishing between these two paths, the motion of the atom is indeterminate and the atom moves in a superposition of both paths. The atom paradoxically moves towards the mirror and away from the mirror at the same time.

The research extends Einstein’s recoiling slit experiment, in which a particle hits a plate with two slits and passes through both slits simultaneously, due to its wave-like quantum mechanical properties.

Ref.: Jörg Schmiedmayer & Markus K. Oberthaler et al., Single spontaneous photon as a coherent beamsplitter for an atomic matter-wave, Nature Physics, April 3, 2011