Nonequilibrium Dynamics of Ultracold Neutral Plasmas

In a number of recent experiments ultracold plasmas (UNPs) have been produced by photoionizing laser-cooled atomic ensembles [1]. Their very low initial kinetic energies suggest that they are created deeply in the strongly correlated regime. Moreover, UNPs are produced far from equilibrium, leading to a complex relaxation dynamics. We present a hybrid-molecular dynamics approach [2], to describe the long-time plasma evolution while fully taking into account the strongly correlated character of the ionic motion. We demonstrate that the method yields an accurate description of recent measurements [2,3] and allows to address problems beyond present experimental capabilities [3]. It turns out that under the conditions in UNPs the commonly applied Bogoliubov assumption about a hierarchy of relaxation timescale becomes invalid, resulting in an unusual relaxation dynamics connected with a wave-like temperature evolution and an ultimate relaxation to a non-equilibrium undercorrelated state.\\ (1) Y.C. Chen et al., Phys. Rev. Lett. 93, 265003 (2004).\\ (2) T. Pohl, T. Pattard and J.M. Rost, Phys. Rev. A 70, 033416 (2004).\\ (3) T. Pohl, T. Pattard and J.M. Rost, Phys. Rev. Lett. 94, 205003 (2005); Phys. Rev. Lett. 92, 205003 (2004).