Measurement of the6S→7SM1transition in cesium with the use of crossed electric and magnetic fields

The forbidden $6S\to 7S$ magnetic dipole transition amplitude in cesium has been measured by laser spectroscopy of an atomic beam in crossed electric and weak magnetic fields. The $M1\mathrm{}$ amplitude was determined by observing the change in the transition rate caused by interference with a Stark-induced $E1\mathrm{}$ amplitude. The result for the nuclear-spin-independent amplitude is -42.10(80) × ${10}^{-6\mathrm{}}$ ${\mathrm{\mu }}_{\mathrm{B}}$, the result for the nuclear-spin-dependent amplitude is 7.59(55) × ${10}^{-6\mathrm{}}$ ${\mathrm{\mu }}_{\mathrm{B}}$. 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.