Dynamically crossing diabolic points while encircling exceptional curves: A programmable symmetric-asymmetric multimode switch

Abstract

Nontrivial spectral properties of non-Hermitian systems can lead to intriguing effects with no counterparts in Hermitian systems. For instance, in a two-mode photonic system, by dynamically winding around an exceptional point (EP) a controlled asymmetric-symmetric mode switching can be realized. That is, the system can either end up in one of its eigenstates, regardless of the initial eigenmode, or it can switch between the two states on demand, by simply controlling the winding direction. However, for multimode systems with higher-order EPs or multiple low-order EPs, the situation can be more involved, and the ability to control asymmetric-symmetric mode switching can be impeded, due to the breakdown of adiabaticity. Here we demonstrate that this difficulty can be overcome by winding around exceptional curves by additionally crossing diabolic points. We consider a four-mode $${{{{{{{\mathcal{PT}}}}}}}}$$ PT -symmetric bosonic system as a platform for experimental realization of such a multimode switch. Our work provides alternative routes for light manipulations in non-Hermitian photonic setups.

Twins of Exceptional Points with Opposite Chirality for Non-Hermitian Metasurfaces

“…Metasurfaces, composed of two-dimensional subwavelength meta-structures, can be regarded as a non-Hermitian system when loss (such as scattering loss, Ohmic loss) in the metasurface plays a considerable role. − Non-Hermitian systems have the intriguing property of exhibiting a distinctive singular point known as an exceptional point (EP), where the eigenvalues and eigenvectors coalesce. − The EPs are involved with sharp phase transitions in the eigenvalue spectrum that can give rise to unconventional responses of the system. − Metasurfaces provide an ultrathin and multifunctional optical platform for non-Hermitian systems that could significantly expand the capabilities to manipulate electromagnetic waves via engineering its microscopic subwavelength meta-structures. − Rich physics and appealing applications around EPs have been realized, for example, unidirectional propagation, − polarization control, − coherent perfect absorption, − ultrasensitive sensing and biosensors, − imaging, − and lasers. − …”