Applications of Exceptional Points in Photonics and AMO
Exceptional points (EPs) are exotic degeneracies in non-Hermitian systems. Due to their counterintuitive properties and recent realizations, EPs have been the focus of immense attention. In this talk, I will present three new applications of EPs: (I) Enhancing spontaneous emission (SE) near EPs [1-3], (II) controlling atomic and molecular absorption , and (III) creating topological mode switches using open quantum systems. I will begin by presenting our formula for the SE spectrum near EPs, where standard mode-expansion methods lead to erroneous and divergent results. I will further show that significant SE enhancements can occur in systems with gain (exceeding 400×). In the second part of the talk, I will present a method for optically inducing EPs in atomic systems, and show that slight changes in the laser parameters may lead to either dramatic enhancement or to complete inhibition of the absorption. Finally, I will describe the intriguing properties of topological mode switches in open quantum systems. When varying a system slowly along a closed path, an adiabatic system returns to its initial state - unless the path encircles an isolated EP, in which case the initial and final states switch. However, non-Hermitian systems do not always evolve adiabatically, and the outcome of the switch depends on the chirality of the path. We explore asymmetric mode switching in open quantum systems, which offer a rich EP structure, including high-order isolated and embedded EPs.
 A Pick, B Zhen, OD Miller, CW Hsu, AW Rodriguez, M Soljacic, and SG Johnson, “General theory of spontaneous emission near exceptional points,” Opt. Express. 25, 12325 (2017)
 Z Lin, A Pick, M Loncar, and AW Rodriguez, Inverse design of third-order Dirac exceptional points in photonic crystals. Phys. Rev. Lett. 117, 107402 (2017)
 A Pick, Z Lin, and, AW Rodriguez, “Enhanced nonlinear frequency conversion and Purcell enhancement at exceptional points,” Phys. Rev. B 96, 224303 (2017)
 A Pick, PR Kapralova-Zdanska, and N Moiseyev, “Optical absorption in atoms and molecules near laser-induced exceptional points,” arXiv: 1809.02868 (2018)