TEST OF THE LINEARITY OF QUANTUM-MECHANICS IN AN ATOMIC SYSTEM WITH A HYDROGEN MASER

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 3.7×1020 eV (8.9 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. © 1990 The American Physical Society.