From Lamb shift to light shifts: Vacuum and subphoton cavity fields measured by atomic phase sensitive detection

M. Brune; P. Nussenzveig; F. Schmidt-Kaler; F. Bernardot; A. Maali; J. M. Raimond; S. Haroche

doi:10.1103/PhysRevLett.72.3339

From Lamb shift to light shifts: Vacuum and subphoton cavity fields measured by atomic phase sensitive detection

M. Brune, P. Nussenzveig, F. Schmidt-Kaler, F. Bernardot, A. Maali, J. M. Raimond, and S. Haroche

Phys. Rev. Lett. 72, 3339 – Published 23 May 1994

Abstract

We have measured by Ramsey interferometry the dispersive light shifts produced on circular Rydberg states by very weak nonresonant microwave fields in a single cavity mode. This experiment yields an absolute measurement of mean photon numbers with a sensitivity of 0.1. The vacuum induced Lamb shift, equal to the light shift of ‘‘half a photon,’’ has been observed, providing a direct and absolute measurement of the zero-point field fluctuations in a cavity mode.