Thomas Pattard

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We present long-time simulations of expanding ultracold neutral plasmas, including a full treatment of the strongly coupled ion dynamics. Thereby, the relaxation of the expanding laser-cooled plasma is studied, taking into account elastic as well as inelastic collisions. It is demonstrated that, depending on the initial conditions, the ionic component of(More)
We investigate the strongly correlated ion dynamics and the degree of coupling achievable in the evolution of freely expanding ultracold neutral plasmas. We demonstrate that the ionic Coulomb coupling parameter Gamma(i) increases considerably in later stages of the expansion, reaching the strongly coupled regime despite the well known initial drop of(More)
Recent experiments with ultracold neutral plasmas show an intrinsic heating effect based on the development of spatial correlations. We investigate whether this effect can be reversed, so that imposing strong spatial correlations could in fact lead to cooling of the ions. We find that cooling is indeed possible. It requires, however, a very precise(More)
We develop a theoretical approach for the dynamics of Rydberg excitations in ultracold gases,with a realistically large number of atoms. We rely on the reduction of the single-atom Bloch equations to rate equations, which is possible under various experimentally relevant conditions. Here, we explicitly refer to a two-step excitation scheme. We discuss the(More)
We provide a detailed theoretical and experimental study of the idea that adding Rydberg atoms to an ultracold plasma may be used as a means of controlling the electronic temperature of the plasma. We show that a certain amount of control is indeed possible, and discuss limitations for the extent of electron cooling. Experimental data are found to be in(More)
It is shown that the two-step excitation scheme typically used to create an ultracold Rydberg gas can be described with an effective two-level rate equation, greatly reducing the complexity of the optical Bloch equations. This allows us to efficiently solve the many-body problem of interacting cold atoms with a Monte Carlo technique. Our results reproduce(More)
It is shown that recently measured cross sections for double ionization of negative ions (H−, O−, and C−) possess a universal shape when plotted in suitable dimensionless units. The shape can be represented with a simple analytical function, following the same principles as it has been done in establishing a universal shape function for single ionization(More)
Recent experiments with ultracold neutral plasmas show an intrinsic heating effect based on the development of spatial correlations, which has been termed “correlation heating”. We investigate whether this effect can be reversed, so that imposing strong spatial correlations could in fact lead to cooling. We find that cooling is indeed possible. It requires,(More)