Cold Rydberg Atoms

Abstract

Abstract We employ ensembles of cold Rydberg-atom gases produced via photo-excitation of laser-cooled atom clouds in order to investigate collision-induced dynamics, excitation blockades, and Rydberg-atom trapping. After a general description of typical experimental methods used in this research, we review state-mixing and ionizing collision processes that have been observed in dense, cold Rydberg atom ensembles excited with broad-band (bandwidth 15 GHz) laser pulses. We then discuss how inter-atomic forces lead to Penning-ionizing collisions between Rydberg atoms and to the partial conversion of internal energy to center-of-mass energy. By exciting Rydberg-atom samples using narrow-band laser pulses (bandwidth 5 MHz), we create many-body states in which Rydberg excitations are coherently shared among several atoms. In this domain, van der Waals and electric–dipole interactions between Rydberg atoms give rise to an excitation blockade. We describe the implications of the blockade on the probability distribution of the number of Rydberg excitations that can be created in small atom ensembles. As a signature of the blockade, sub-Poissonian distributions of the Rydberg-atom number are presented. We further review possible methods of Rydberg-atom trapping in static electric and magnetic fields and in optical fields. A recent experimental demonstration of Rydberg-atom trapping in a Ioffe–Pritchard trap with a central magnetic field of 2.9 Tesla is discussed. The strongly magnetized Rydberg atoms we have trapped using this apparatus are atoms in long-lived, high-angular momentum states which are populated via Rydberg-atom collisions. We also present results on the photo-, electric-field-, and auto-ionization of cold, strongly magnetized Rydberg atoms.