On October 30, Prof. Lin Chen from Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Prof.Cheng-Wei QiufromNational University of Singapore,Prof.Andrea Alù from City University of New York published new advances in PHYSICAL REVIEW LETTERS. The paper is entitled "Hamiltonian Hopping forEfficientChiral Mode Switching in Encircling Exceptional Points".
Exceptional points are intriguing degeneracies arising in non-Hermitian coupling systems. In the Hamiltonian parameter space composed of loss difference and coupling detuning, asymmetric transition can be realized by constructing an evolution path that encircles the exceptional point. However, the system statessufferfrom path-dependent losswithconventional evolutions, and the final output energy is extremely low.
The researchers found that the eigenstates of the system converge to the same value when the Hamiltonian parameters approach to infinite. In addition, one of the eigenstates is lossless, which means that a low-loss evolution path around exceptional point can be designed. Because of the same converged eigenstates, the “Hamiltonian hopping” is enabled on the parameter space boundaries with infinite parameter, which reduces both the system loss and the total evolution time. The final state is different for reverseevolution path, and it only depends on the encircling direction, no matter which eigenstate is chosen as the starting state. The required Hamiltonian parameters for Hamiltonian-hopping-assisted loop around exceptional point can be mapped onto suitably designed purely lossy silicon coupled waveguides. Efficient asymmetric transmission is achieved for the 0-order and 1-order coupling modes. The proposed protocol can achieve in principle near-unity transmission efficiency over the entire telecommunication spectrum form 1200-1700nm due to the robustness against the encircling pathway, and the researchers experimentally demonstrate nearly 90% efficiency at 1550 nm.The presented results suggest a promising yet robust approach to tackle the long-standing loss issue in non-Hermitian dynamics, impacting numerous studies on EP in optics, acoustics, electronics and condensed matter physics.
This work was supported by the National Natural Science Foundation of China and National Major Research and Development Program. This paper is jointly collaborated with Dr. Aodong Li, Prof.Jianji Dong,Prof.Jian Wang, Dr. Ziwei Cheng, Prof.Lin Chen from Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Prof.John S. Ho,Prof.Cheng-Wei QiufromNational University of Singapore,Prof.Dawei Zhang,Prof.Jing Wen fromUniversity of Shanghai for Science and Technology,Prof.Xu-Lin Zhang fromJilin University,Prof.C. T. Chan fromThe Hong Kong University of Science and Technology, andProf.Andrea Alù from City University of New York.
Address: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.187403
FIG.1 Hamiltonian-hopping-assisted loop around exceptional point for (a) clockwise and (b) anticlockwise directions. (c) The corresponding silicon coupled optical waveguides.
FIG.2 Field distributions of encircling exceptional point for (a) clockwise and (b) anticlockwise directions. (c) Simulated and (d) measured transmittance spectra.
