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Test of the linearity of quantum mechanics in an atomic system with a hydrogen maser
Ronald Lee Walsworth (Harvard University), Isaac F. Silvera (Harvard University), Edward M. Mattison (Harvard University, Smithsonian Astrophysical Observatory), Robert F. C. Vessot (Harvard University, Smithsonian Astrophysical Observatory)
Abstract: We extend a nonlinear generalization of quantum mechanics, recently formulated by Weinberg, to systems of composite spin, such as atoms. We have used hydrogen (H) masers to set a limit of 3.7\ifmmode\times\else\texttimes\fi{}${10}^{20}$ eV (8.9 \ensuremath{\mu} Hz) on the magnitude of a nonlinear correction to the quantum mechanics of atomic spins. This result is of comparable magnitude to the limit recently set in a single-valued (nuclear) spin system. In the absence of nonlinear effects, the experiment provides a new and stringent test of H-maser clock performance and the applicability of standard maser theory.