  We calculate the gravitational-electromagnetic phase for a charged particle
in the Kerr-Newman spacetime. The result is applied to an interference
experiment, in which the phase differences and the fringe shifts are derived.
We find that both the charge of the particle and the charge of the black hole
contribute to the gravitational phase difference, for which we give some
qualitative explanations. Finally, we extend the results to the case of dyonic
particles in the spacetime of a dyonic Kerr-Newman black hole.
