Abstract: By confining a diffusion atom in a nanometer region using surface potential heterogeneity we have successfully employed time-dependent tunneling spectroscopy to study its random motion quantitatively. A hopping rate in the range of 1—10000Hz, approximately 3 orders of magnitude faster than those accessible by existing diffusion methods based on scanning tunneling microscopy, was demonstrated for single Cu atoms diffusing in the faulted half-unit cell of Si(111)-7×7. Our technique is potentially useful for detecting fast diffusion processes such as hydrogen quantum diffusion on the atomic scale.