Rings and Boxes in Dissipative Environments

We study a particle on a ring in presence of a dissipative Caldeira-Leggett environment and derive its response to a dc field. We find, through a 2-loop renormalization group analysis, that a large dissipation parameter eta flows to a fixed point eta(R) = eta(c) = h/2 pi. We also reexamine the mapping of this problem to that of the Coulomb box and show that the relaxation resistance, of recent interest, is quantized for large eta. For finite eta > eta(c) we find that a certain average of the relaxation resistance is quantized. We propose a box experiment to measure a quantized noise.