We are studying high energy density physics in extreme states theoretically with a help of computer simulations. High energy density states with high temperatures and high densities are the states equivalent to the inside of planets or stars. In laboratory, we can create such extreme states using intense laser lights. In the high energy density states, matters are fully or partially ionized, and plasmas accompanying high energy particles and radiations are created. High energy density plasmas are therefore complex systems which have various energy transfer processes among particles, photons, and electromagnetic fields. We are aiming to understand physics in the high energy density plasmas which helps comprehending the phenomena of the interior of stars and contributing to realize laser-based particle accelerators and fusion energy. We make use of super computer simulations to develop theoretical models for the complicated plasma phenomena. Simulations are virtual experiments in computers, so that your imagination is a key for the research.<\/p>\n