Atomic Tunneling from a STM/AFM Tip: Dissipative Quantum E ects from Phonons

We study the eeects of phonons on the tunneling of an atom between two surfaces. In contrast to an atom tunneling in the bulk, the phonons couple very strongly, and qualitatively change the tunneling behavior. This is the rst example of ohmic coupling from phonons for a two-state system. We propose an experiment in which an atom tunnels from the tip of an STM, and show how its behavior would be similar to the Macroscopic Quantum Coherence behavior predicted for SQUIDS. The ability to tune and calculate many parameters would lead to detailed tests of the standard theories.