Towards a New Quantum Frontier in High Energy Density Science

未来几年，新的设施发展将改变我们在温度、密度和压力的极端条件下探索物质的能力。高能激光的进步，以及它们在大规模自由电子激光设施中的共处位置，例如汉堡的欧洲XFEL，将很快使我们能够例行公事地将物质驱动到超过10兆巴的压力，并用地球上最亮的X射线源探测它。在美国，LCLS-II设施的建设将使独立的X射线泵和X射线探测器实验能够首次进行。这些能力将支持在纳米尺度和超短时间尺度上对恒星内部和行星外核心条件下的物质进行新颖的实验室研究。最耐人寻味的是，这些进展有望提供进入奇异等离子体区域的途径，在那里量子行为被转移到宏观尺度，构成了高能量密度科学中的一个新的量子前沿。在这里，我们建议开发一个实验计划来研究这一前沿。通过使用时间分辨、共振非弹性x射线散射，我们将首先开发在基于实验室的行星天体物理实验中测量温度和价电子结构的有效方法。然后，我们的目标是在越来越高的密度下，在核心-电子相互作用变得重要的系统中，时间分辨电子局域化动力学。在此背景下，我们将研究这种电子相互作用如何有助于缓解或抑制相变、金属有序，以及支持在高压缩下产生复杂结构的机制，如电子三元。最后，我们的目标是通过寻找原分子系统中瞬时原子间键的存在，并在超快时间尺度上探索它们的核动力学，来探索高能量密度量子等离子体是否能够支持核心化学，即内电子的杂化和成键。

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.