Realization of exceptional points along a synthetic orbital angular momentum dimension

Abstract

Exceptional points (EPs), at which more than one eigenvalue and eigenvector coalesce, are unique spectral features of Non-Hermiticity (NH) systems. They exist widely in open systems with complex energy spectra. We experimentally demonstrate the appearance of paired EPs in a periodical driven degenerate optical cavity along the synthetic orbital angular momentum (OAM) dimension with a tunable parameter. The complex-energy band structures and the key features of EPs, i.e. their Fermi arcs, parity-time symmetry breaking transition, energy swapping, and half-integer band windings are directly observed by detecting the cavity's transmission spectrum. Our results advance the fundamental understanding of NH physics and demonstrate the flexibility of using the photonic synthetic dimensions to implement NH systems.

Simulating topological materials with photonic synthetic dimensions in cavities

“…By drilling a hole on the wave plate, a sharp boundary can be created [55]. By introducing different loss on different polarizations, the exceptional points can be realised [52]. Moreover, Weyl semimetal phases and implementation can be obtained along the synthetic OAM dimension in degenerate optical cavities [56].…”

“…Moreover, we can get the details of the energy bands by using wavefront angle-resolved band structure spectroscopy [52]. We need to project the output photons on the base |k k|, where |k = m e -imk |m is the Bloch state along OAM lattice.…”