DEPHASING AND THE ORTHOGONALITY CATASTROPHE IN TUNNELING THROUGH A QUANTUM-DOT - THE WHICH PATH INTERFEROMETER

The ''Which Path?'' interferometer consists of an Aharonov-Bohm ring w ith a quantum dot (QD) built in one of its arms, and an additional qua ntum point contact (QPC) located close to the QD. The transmission coe fficient of the QPC depends on the charge state of the QD. Hence the p oint contact acts as a controllable measurement device for which path an electron takes through the ring. We calculate the suppression of th e Aharonov-Bohm oscillations which is caused by both measurement depha sing and the orthogonality catastrophe, i.e., respectively, by real an d virtual electron-hole pair creation at the QPC. [S0031-9007(97)04496 -7].