報告題目：Novel Electromagnetic Scattering Phenomena
時間：7 月 2 日（星期二） 上午 10:30-
主講人簡介：Yi Yang is a graduate of Electrical Engineering at
PekingUniversity,BSc & MSc. Since 2014,Yihas been a PhD student in the group of Prof. Marin Solja?i? at Massachusetts Institute ofTechnology(MIT), studying photonics and plasmonics. He will become a postdoctoral associate in the same group starting 2019 fall.
報告摘要：Scattering of electromagnetic waves is fundamentally
related to the inhomogeneity of a system. He will describe his recent theoretical and experimental findings of electromagnetic scattering under contemporary context. First, he will discuss a universal upper limit to the spontaneous free electron radiation and energy loss . Such an upper limit allows them to make two predictions. One is a new regime of radiation operation—at subwavelength separations, slower (non-relativistic) electrons can achieve stronger radiation than fast (relativistic) electrons. The other is a divergence of the emission probability in the limit of lossless materials. They further reveal that such divergences can be approached by coupling free electrons to photonic bound states in the continuum. Second, he will present a general framework for nanoscale electromagnetism . The framework is featured by surface response functions known as Feibelman d-parameters, which allows a straightforward account of surface-related nanoscale, quantum corrections. Experimentally, they introduces the ‘ellipsometry’ for the surface response functions, enabled by the observation of large nonclassical spectral shifts and the breakdown of Kreibig broadening.
Finally, he will discuss a synthesis and observation of non-Abelian (non-commutative) guage fields in real space . Via a real-space closed loop configuration, they observe the non-Abelian Aharonov–Bohm effect with classical waves and classical fluxes. Based on optical mode degeneracy, they break time-reversal symmetry in different manners—via temporal modulation and the Faraday effect—to synthesize tunable non-Abelian gauge fields. The Sagnac interference of two final states, obtained by reversely-ordered path integrals, demonstrates the non-commutativity of the gauge fields. These results introduce real-space building blocks for non-Abelian gauge fields, relevant for classical and quantum exotic topological phenomena.
 Yi Yang,AviramMassuda, Charles Roques-Carmes, Steven E. Kooi, Thomas Christensen, Steven G. Johnson, John D. Joannopoulos, Owen D. Miller, Ido Kaminer & Marin Solja?i?, Maximal spontaneous photon emission and energy loss from free electrons, Nature Physics,14, 894 (2018)
 YiYang,Di Zhu,Wei Yan,Akshay Agarwal, Mengjie Zheng, John D. Joannopoulos, Philippe Lalanne, Thomas Christensen, Karl K. Berggren, Marin Solja?i?, A General Theoretical and Experimental Framework for Nanoscale Electromagnetism, arXiv: 1901.03988 (2019)
 Yi Yang,Chao Peng, Di Zhu, Hrvoje Buljan, John D. Joannopoulos, Bo Zhen, and Marin Solja?i?, Synthesis and Observation of Non-Abelian Gauge Fields in Real Space, arXiv: 1906.03369 (2019)