Measurement of the 6S → 7S M1 transition in cesium with the use of crossed electric and magnetic fields

The forbidden 6S→7S magnetic dipole transition amplitude in cesium has been measured by laser spectroscopy of an atomic beam in crossed electric and weak magnetic fields. The M1 amplitude was determined by observing the change in the transition rate caused by interference with a Stark-induced E1 amplitude. The result for the nuclear-spin-independent amplitude is −42.10(80) × 10⁻⁶ μ_B; the result for the nuclear-spin-dependent amplitude is 7.59(55) × 10⁻⁶ μ_B. These values disagree with earlier measurements but they are in good agreement with theory. The experimental approach is well suited to measuring parity-violating neutral-current interactions.