PT-symmetry and non-Hermitian physics in polariton condensates in semiconductor microcavities

• Applicant: Dr. Xuekai Ma
• Subject Area: Theoretical Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 467358803

Non-Hermitian physics has attracted significant attention because many unique and unconventional properties have been observed. In a physical system described by a non-Hermitian Hamiltonian, parity-time (PT) symmetry can lead to a real-valued energy spectrum, which becomes complex-valued when the PT-symmetry is broken. In previous work, the study of non-Hermitian physics often focused on optical systems, where enormous progress has been made. Recently, the non-Hermitianity has also been reported for exciton polaritons which are quasi-particles composed of photons and excitons. Polaritons in planar microresonators have also attracted a lot of attention due to their potential application in all-optical circuits, low-threshold lasers, information processing, and light propagation control. In the proposed project, we will investigate the non-Hermitian physics of polaritons in a macroscopically coherent (condensed) state with an emphasis on the following four aspects. Firstly, the polaritons will be loaded into coupled micro-pillars. We will study the resulting nonlinear Josephson dynamics in the presence of non-Hermitian potentials. Secondly, PT-symmetry will be studied in 1D chain lattices. By adjusting the relative position of the chain lattice and the excitation pump, the optically induced imaginary potential can be efficiently modulated. New properties are expected to be observed in the PT-symmetry and PT-symmetry breaking regimes. Thirdly, the possibility of realization of PT-symmetry in a ring potential will be investigated. It is expected that when the loss and gain reach a critical value, the propagation of polaritons in the ring potential can undergo a jamming anomaly, which is essential for realizing a polariton circuit. We will also investigate the impact of the exceptional points on the spatial modes. Lastly, we will focus on the bandstructure of polaritons in hexagonal lattices and investigate the properties close to the Dirac point. Modulating the excitation pump enables the realization of PT-symmetry in a hexagon structure and also Moire patterns can be realized. We will focus on the theoretical study and numerical simulation of the physics outlined above and our cooperation partner will focus on the experimental realization. The results of our project will significantly extend the scope of non-Hermitian physics previously mostly studied in linear optical systems, enable potential new applications of polaritons in functional polaritonic device concepts, and draw attention to the study of non-Hermitian physics, polariton physics, and nonlinear optics in general.

• DFG Programme: Research Grants
• International Connection: China
• Co-Investigator: Professor Dr. Stefan Schumacher
• Cooperation Partner: Professor Dr. Tingge Gao