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 dimension with a tunable parameter. The complex-energy band structures and the key features of EPs, i.e., their bulk Fermi arcs, parity-time symmetry breaking transition, energy swapping, and half-integer band windings, are directly observed by detecting the wavefront angle–resolved transmission spectrum. Our results demonstrate the flexibility of using the photonic synthetic dimensions to implement NH systems beyond their geometric dimension and EP-based sensing.

Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives

“…g) Various N‐containing functional groups in graphene. [ 439 ] Copyright 2017 The Authors. h) The schematic of all N dopant types and defect types for DFT calculations.…”

“…The controllable preparation of defects in CAC materials becomes a reality when a specific N configuration (pyridine‐N, graphite‐N, or pyrrole‐N) corresponds to the topological defect configuration (Figure 12g). [ 439 ] The carbon lattice is disrupted by the introduction of N atoms, and the N‐doped samples are effectively converted into defects after zinc‐induced edge‐engineered hydrothermal treatment, and thermogravimetric analysis yields the release of N atoms in whatever form they are present in the carbon structure without loss of carbon atoms, leaving only new reconfigured defects. The graphite‐N atom is bonded to three neighboring carbon atoms inside the perfect carbon matrix, and the single vacancies created after the removal of the high energy input migrate and merge into highly stable double vacancies (C585).…”

Unveiling the Potential of Covalent Organic Frameworks for Energy Storage: Developments, Challenges, and Future Prospects

“…Supercapacitor electrodes benefit largely from using porous nanocarbons, graphene, and conducting polymeric materials that are rich in nitrogen. [ 353 ] However, for the electrode materials to be able to act efficiently requires high N doping concentration and large SSAs. For these reasons, the linkers with high N content can enrich the COF backbones and then, after pyrolysis, nanostructures can be obtained by combining the high concentration of N‐center sites with the high porosity of the carbon structure.…”

Deep-learning-empowered synthetic dimension dynamics: morphing of light into topological modes

“…Examples include demonstrations of non-Hermitian topological winding, 9,10 skin effect, 11 parity-time symmetry, 12,13 topological "triple" phase transition, 14 and nontrivial topology arising from a system's dissipation. 15 Thus far, SDs have been constructed using a variety of parameters or degrees of freedom in a given system, such as frequency modes, spatial modes, orbital angular momenta, and time-delayed pulses, 11,[14][15][16][17][18][19][20][21][22] along with many proposed applications in, for example, optical communications and topological insulator lasers. 23,24 One highly desirable goal of these studies is to construct a "utopian" network of resonators or coupled modes, where any pair of modes could be coupled in a controlled fashion.…”