TEST OF THE LINEARITY OF QUANTUM-MECHANICS IN OPTICALLY PUMPED HG-201

Measurement of the free precession of nuclear spins in optically pumped ground-state Hg201 atoms has allowed a test of Weinberg's nonlinear generalization of quantum mechanics. Shifts among the three resolved precession frequencies in the spin-3/2 system were studied as a function of the projection of spin polarization along the precession axis. Our results set an upper limit on μ, Weinberg's nonlinearity parameter, of Latin small letter h with stroke<3.8 Hz, which corresponds to 2.0×10-27 of the binding energy per nucleon. This is the most stringent such limit to date. © 1990 The American Physical Society.