Magnetic Johnson noise constraints on electron electric dipole moment experiments

Magnetic fields from statistical fluctuations in currents in conducting materials broaden atomic linewidths by the Zeeman effect. The constraints imposed by this broadening on the design of experiments that measure the electric dipole moment of the electron are analyzed. Contrary to the predictions of Lamoreaux [S. K. Lamoreaux, Phys. Rev. A 60, 1717 (1999)], the standard material for high-permeability magnetic shields proves to be as significant a source of broadening as is an ordinary metal. A scheme that would replace this standard material with ferrite is proposed.