Coherence and Decoherence in Rydberg Gases

Abstract

Dipole-dipole interactions between cold Rydberg atoms have recently attracted much interest since they play a central role in proposed quantum logic gates [Jaksch 2000; Lukin 2001]. While dipole-dipole interactions between cold, or stationary Rydberg atoms, are only beginning to be explored [Anderson 1998 (b); Mourachko 1998], resonant dipole-dipole collisions between Rydberg atoms have been studied extensively [Gallagher 1992]. The connection between the two phenomena is that the interactions between cold stationary atoms correspond to freezing a pair of colliding atoms at their point of closest approach. In the first section of this article we describe resonant dipole-dipole energy transfer collisions between Rydberg atoms. As we shall see, very subtle features can be discerned in these collisions, and they are a good starting point for the development of an understanding of dipole-dipole interactions in a frozen Rydberg gas. An ensemble of cold Rydberg atoms is easily obtained after laser excitation of a cold atomic cloud, as those performed in a Cs or Rb vapor-cell magnetooptical trap, at a temperature of 135 μK or 300 μK respectively. In the case of cesium (for the experiments performed at Laboratoire Aime Cotton) or rubidium (for the experiment performed at the University of Virginia), the atoms p-excited by the cooling lasers are Rydberg-excited by using a laser pulse provided by a dye laser pumped by the third harmonic of a Nd : Y AG laser