Paul Tanner

Dipole-dipole broadening of Rb ns-np microwave transitions

The dipole-dipole broadening of ns-np microwave transitions of cold Rb Rydberg atoms in a magneto-optical trap has been recorded for 28{<=}n{<=}51. Since the electric dipole transition matrix elements scale as n{sup 2}, a broadening rate scaling as n{sup 4} is expected and a broadening rate of 8.2x10{sup -15}n{sup 4} MHz cm{sup 3} is observed. The observed broadening is smaller than expected from a classical picture due to the spin-orbit interaction in the np atoms. The broadened resonances are asymmetric and cusp shaped, and their line shapes can be reproduced by a diatomic model which takes into account the dipole-dipole interaction, including the spin-orbit interaction, the strengths of the allowed microwave transitions, and the distribution of the atomic spacings in the trap.

Coherence and Decoherence in Rydberg Gases

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