  We have observed a dissipative phase diffusion branch in arrays of hysteretic
high-Tc intrinsic Josephson junctions. By comparing the data with a thermal
activation model we extract the impedance seen by the junction in which phase
diffusion is occurring. At the plasma frequency this junction is isolated from
its environment and it sees its own large (~ kilo Ohm) impedance. Our results
suggest that stacks of Josephson junctions may be used for isolation purposes
in the development of a solid state quantum computer.
