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A molecule standing on a metal surface has been found to emit electrons in the presence of an applied electric field. The emitted electrons produce an interference pattern reminiscent of a classic physics experiment.
Quantum systems are described by wavefunctions, which have an amplitude and a phase: the square of the amplitude describes the probability of finding a particle in a given region of space-time, whereas the phase describes the sign (plus or minus) of the wavefunction. The ability to control the phase of systems of electrons would open up opportunities for the development of quantum devices, and the first step in achieving such control is to ascertain what the phase is in the first place. Unfortunately, the phase of an object’s wavefunction is not directly observable. It is, however, possible to work out the relative phase by observing interference patterns formed from the superposition (summation) of coherent electron waves (those between which there is a constant phase difference), by borrowing schemes from classic experiments that observed interference patterns in light, such as Thomas Young’s ‘double-slit’ experiment1 or Dennis Gabor’s demonstration of holography2. Writing in Nature, Esat et al.3 report a tabletop experiment that allows the phase of a molecular orbital to be determined from an interference pattern that arises as a result of electron emission from the molecule concerned.