PerspectiveQuantum Mechanics

Interference of atomic clocks

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Science  11 Sep 2015:
Vol. 349, Issue 6253, pp. 1168-1169
DOI: 10.1126/science.aad0683

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When de Broglie predicted that we need to associate a periodic phenomenon with any isolated portion of matter or energy (1), this idea became the basis of Schrödinger's wave equation and modern matter-wave interferometry. It has stood the test of time and inspired intriguing discussions on the relation between quantum physics, classicality (2), and general relativity theory (GRT) (35). It also inspired the recent work on page 1205 of this issue by Margalit et al. (6), who demonstrated that the internal clock of a delocalized atom can be used as a witness of the atom's path through a matter-wave interferometer. The study shows Bohr's complementarity principle in action and how dephasing in an external potential may mimic “classicality” even though the underlying quantum correlations can be erased and reversed.