1. L. P. Kouwenhoven, T. H. Oosterkamp, M. W. S. Danoesastro, Department of Applied Physics and Delft Institute of MicroElectronics and Submicrontechnology, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, Netherlands.
2. M. Eto, Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223, Japan.
3. D. G. Austing, T. Honda, S. Tarucha, NTT Basic Research Laboratories, 3-1, Morinosoto Wakamiya, Atsugi-shi, Kanagawa 243-01, Japan.