Quasinormal modes in optics and mechanics: from Fano resonances to new insights in quantum optics - Stephen Hughes

Quasinormal modes (QNMs) are decaying modes of open cavity systems, with complex eigenfrequencies and spatially diverging modes. Historically, QNMs have been used to describe modes in “dirty black holes” and were scarcely even mentioned in optics. In recent years, however, QNMs they have become an extremely powerful tool for describing light-matter and force-mechanical interactions in an efficient and accurate way [1-3], and offer one of the only rigorous ways of quantizing fields in open cavity systems. While the workhorse formalism for cavity physics has been to use a “normal mode” description, for cavity modes, such an approach fails to properly account for dissipation and the phase of the mode. This talk will discuss some of the recent developments of QNMs in both optics and mechanics. Various applications will be shown, including QNMs for plasmonics, hybrid dielectric-metal systems and the elastic Purcell formula. Finally, I will also present some recent results on how to fully quantize these QNMs [4], which introduces some fundamentally new concepts in quantum optics and clearly demonstrates the limits and failure of Jaynes–Cummings type models.

[1] Philip Trost Kristensen and Stephen Hughes, Modes and Mode Volumes of Leaky Optical Cavities and Plasmonic Nanoresonators, ACS Photonics 1, 2 (2014). [2] Mohsen Kamandar Dezfouli, Reuven Gordon, and Stephen Hughes, Modal theory of modified spontaneous emission of a quantum emitter in a hybrid plasmonic photonic-crystal cavity system, Phys. Rev. A 95, 013846 (2017). [3] Al-Waleed El-Sayed and Stephen Hughes, Quasinormal mode theory of elastic Purcell factors and Fano resonances of optomechanical beams, arXiv:2006.14809 (2020). [4] Sebastian Franke, Stephen Hughes, et al., Quantization of quasinormal modes for open cavities and plasmonic cavity-QED, Phys. Rev. Lett. 122, 213901 (2019); Sebastian Franke, Marten Richter, Juanjuan Ren, Andreas Knorr, and Stephen Hughes, Quantized quasinormal mode description of non-linear cavity QED effects from coupled resonators with a Fano-like resonance, arXiv:2006.04506 (2020).