In September 2019, Dr. Xuekai Ma, a young scientist from Prof. Stefan Schumacher’s group, spent a month’s research visit with Prof. Yaroslav Kartashov in Prof. Lluis Torner’s group at the Institute of Photonic Sciences (ICFO) in Barcelona, Spain.
In their ongoing collaboration with Prof. Kartashov, the team recently proposed a novel concept to achieve parity-time (PT) symmetry in exciton-polaritons in a semiconductor micro resonator. The key ingredient to achieve PT symmetry in this system is the simultaneous application of a periodically modulated optical laser and a periodically modulated acoustic wave. The theoretical results were published in the New Journal of Physics  (see the figure to the right).
During his stay at ICFO, Dr. Ma experienced an exciting and inviting research environment with plenty of fruitful discussions in which a number of promising new ideas for future research endeavors were conceived. For instance, rotating vortices with helical trajectories in time were predicted during his visit and demonstrated numerically. In the future, experimental efforts along these lines will be undertaken as part of the TRR142 project A04 with Prof. Marc Aßmann from the TU Dortmund. In this successful collaboration, one of Dr. Ma’s theoretical proposals on all-optical vortex switching in polariton condensates was recently experimentally realized  by TRR142 PhD student Bernd Berger from the TU Dortmund. The results obtained are of general interest for all-optical information processing with functional photonic circuits.
 X. Ma, Y. Y. Kartashov, T. Gao, and S. Schumacher, “Controllable high-speed polariton waves in a PT-symmetric lattice”, New Journal of Physics (2019). https://doi.org/10.1088/1367-2630/ab5a9b
 X. Ma, B. Berger, M. Assmann, R. Driben, T.Meier, C. Schneider, S. Höfling, and S. Schumacher, “Realization of all-optical vortex switching in exciton-polariton condensates”, arXiv: 1907.03171 (2019).