Towards a New Quantum Frontier in High Energy Density Science

Novel facility developments over the next few years are set to transform our ability to explore matter in extreme conditions of temperature, density and pressure. Advances in high-energy lasers, and their co-location at large-scale free-electron laser facilities, such as the European XFEL in Hamburg, will soon allow us routinely to drive matter to pressures exceeding 10 Mbar, and probe it with the brightest x-ray source on the planet. In the US, the construction of the LCLS- II facility will enable independent x-ray-pump, x-ray-probe experiments to take place for the very first time. These capabilities will support novel laboratory-based studies of matter in stellar interior and exoplanetary core conditions, at the nanoscopic scale, and on ultrashort timescales. Most intriguingly, these advances promise to provide access to exotic plasma regimes where quantum behaviour is transferred to the macroscale, constituting a new quantum frontier in high-energy- density science. Here we propose to develop an experimental program to investigate this frontier. By using time-resolved, resonant inelastic x-ray scattering, we will firstly develop efficient approaches to measuring temperatures and valence electronic structure in laboratory-based planetary astrophysics experiments. We then aim to time-resolve electron localization dynamics in systems at increasingly high densities, where core-electron interactions become important. In this context we will study how such electron interactions help mitigate or inhibit phase transitions, metallic ordering, and support mechanisms driving the creation of complex structures such as electrides at high compression. Finally, we aim to explore whether high-energy-density quantum plasmas are able to support core-chemistry, i.e., hybridization and bonding of inner-electrons, by searching for the presence of transient interatomic bonds in proto-molecular systems, and probing their nuclear dynamics on ultrafast time scales.