Measuring the geometric component of the transition probability in a two-level system

We describe the measurement of a component of the nonadiabatic transition probability in a two-level system that depends only on the path through parameter space followed by the Hamiltonian, and not on how fast the path is traversed [M. V. Berry, Proc. R. Soc. London 430, 405 (1990)]. We performed the measurement by sweeping a radio-frequency field through the Zeeman resonance of carbon-13 in a static magnetic field and measuring the transition probability P at the end of each sweep. We found that, for appropriately chosen radio-frequency sweep forms, a factor of P is independent of the duration of the sweep, in accordance with the theory of Berry.