Precision measurement: Relativity tested with a split electron.

Abstract

Splitting and recombining an electron wave packet has been used to test relativity at a record sensitivity. The result heralds an era of precision measurements of relativity using quantum-information methods. See Letter p.592 For almost all measurements, physicists assume that the absolute orientation has no influence on the result of the measurement. But certain theories that go beyond the standard model of physics predict that this basic assumption doesn't hold in all cases. In other words, some extensions of the standard model predict violation of Lorentz symmetry. Here, the authors test Lorentz symmetry for electrons, to extremely high precision, using a technique inspired by quantum information science. In a trapped calcium ion, they split an electron wave packet into two parts and recombine them after 0.1 seconds. In that 0.1 seconds, the Earth has rotated slightly and the two parts of the wave packet assume different spatial orientations. Lorentz symmetry violation would change the interference at recombination. In this sense, the experimental procedure is related to the famous Michelson–Morley experiment of 1887, in which the theory of luminiferous aether was disproven. This new measurement allows for an improvement in precision by a factor of 100 over previous measurements, which advances Lorentz symmetry tests towards regimes relevant to extensions of the standard model.