Ultracold Rydberg Gases Research Articles

Coherent excitation of Rydberg atoms in an ultracold gas

We demonstrate two schemes for the coherent excitation of Rydberg atoms in an ultracold gas of rubidium atoms employing the three-level ladder system 5S1/2–5P3/2-nℓj. In the first approach rapid adiabatic passage with pulsed laser fields yields Rydberg excitation probabilities of 90% in the center of the laser focus. In a second experiment two-photon Rydberg excitation with continuous-wave fields is applied which results in Rabi oscillations between the ground and Rydberg state. The experiments represent a prerequisite for the control of interactions in ultracold Rydberg gases and the application of ultracold Rydberg gases for quantum information processing.

Ultracold neutral plasmas and Rydberg gases

We present two different theoretical approaches for the simulation of ultracold plasmas and Rydberg gases, namely a simple kinetic model including an approximate treatment of ionic correlations on the one hand and a hybrid molecular dynamics (MD) approach treating the electrons as a fluid but ions and atoms on a full MD level on the other hand. The simple kinetic model can be used in situations where the number of particles is so large that it prohibits an MD simulation, and, maybe even more importantly, it gives additional insight into the dynamics beyond that possible on the basis of MD simulations by providing simple evolution equations for the macroscopic parameters describing the state of the system. On the other hand, the MD approach provides a powerful method for the study of spatially resolved quantities, and it permits the study of scenarios where the ions are so strongly coupled that Coulomb crystallization occurs, which cannot be described by the kinetic model.

Spectroscopy of an ultracold Rydberg gas and signatures of Rydberg–Rydberg interactions

We report on experiments on Rydberg–Rydberg interaction-induced effects in a gas of 87Rb Rydberg atoms. A compact setup for two-photon continuous-wave excitation of high-lying Rydberg states out of an ultracold atomic gas is presented. The performance of the apparatus is characterized by high-resolution spectroscopy of Rydberg states. Signatures of interaction-induced effects are identified by qualitatively analysing the dependence of Rydberg excitation spectra on the intensity and the duration of the second-step laser excitation.

Plasma formation from ultracold Rydberg gases

Recent experiments have demonstrated the spontaneous evolution of a gas of ultracold Rydberg atoms into an expanding ultracold plasma, as well as the reverse process of plasma recombination into highly excited atomic states. Treating the evolution of the plasma on the basis of kinetic equations, while ionization/excitation and recombination are incorporated using rate equations, we have investigated theoretically the Rydberg-to-plasma transition. Including the influence of spatial correlations on the plasma dynamics in an approximate way we find that ionic correlations change the results only quantitatively but not qualitatively.