---------------------------------------------------------------------------------------------- Project: A10 Title: Collective emission of atoms in high-intensity pulses of an x-ray free electron laser DESY group: FS-TUXS (Theoretical Ultrafast X-ray Science) Type: Remote project Duration: 19th july - 10th sep 2021 Description: The ultrashort high-intensity pulses from x-ray free-electron lasers can drive the matter in novel states. In our group, we investigate the x-ray self-amplifying state that transiently appears after massive inner-shell photoionization. In these conditions, spontaneously emitted x-ray fluorescence develops into collective emission resulting in short and intense x-ray bursts -- that can be used as a spectroscopic tool or as an x-ray source with unique properties. Theoretical description of this process is challenging -- it requires quantum-mechanical treating of the initial stage, dealing with the macroscopic amount of emitters, and accounting for field propagation effects. Within the summer student programme, we propose to start with theoretical modeling of collective emission from few (two-level) atoms -- a solvable case where one can obtain insights into the collective emission process. As a next step, ways to generalize to the macroscopic amount of atoms can be considered and crossover to continuous description can be studied. The results of the project may help in understanding the role of a local arrangement of atoms on collective x-ray emission properties, and could be investigated further jointly. We expect from the candidates the knowledge of quantum mechanics (quantum optics) and basic skills in numerical modeling (e.g., in Python). Special Qualifications expected: Theoretical background and basic knowledge of quantum mechanics are required. Skills in numerical modeling would be beneficial for the project. Link to further information: https://tuxs.desy.de/careers/ Depending on the situation in the summer and the residency of the applicant, this remote project may be converted into an on-site project. ----------------------------------------------------------------------------------------------