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McKelvey School of Engineering

ESE Seminar: Dissertation Defense Changqing Wang

Thursday, May 20 | 10:00 AM - 12:00 PM

Non-Hermitian physics describes the behaviors of open systems which have interactions with the environment. It can be applied to a wide range of classical and quantum systems. Exotic physical phenomena are unveiled in such non-Hermitian systems, especially around a singular point in the parameter space, i.e., the exceptional point (EP), where the eigenvalues and the associated eigenvectors are degenerate. A plethora of demonstrations have been found in optics and photonics, where the non-Hermitian effects are ubiquitous due to the existence of optical dissipation or amplification. In particular, whispering gallery mode (WGM) resonators are ideal candidates for studying light-matter interactions in the non-Hermitian context owning to their ultrahigh optical quality, small mode volume, and great degrees of flexibility in parameter control. Past years have witnessed intriguing demonstrations of non-Hermitian singularities and unconventional effects in WGM resonators, which have shown great potential in photonic applications such as the engineering of lasers, optical sensors and light transport, etc.

In this dissertation, we present our study on non-Hermitian WGM microresonators with a special emphasis on the physical behavior associated with the EPs. First, based on the chirality of optical modes at EPs, we utilize nano scatterers to manipulate the interference effect and control electromagnetically induced transparency (EIT) in a system composed of indirectly coupled WGM resonators. Second, we study the polarization effects on wave transport and show a polarization induced transparency effect which is distinct from EIT. Third, we study novel types of EPs in directly coupled WGM resonators based on the scattering property, and demonstrate exotic behaviors in light absorption enabled by such kinds of EPs. Finally, we investigate the noise behavior and robustness of non-Hermitian optical sensors.

Event Type



McKelvey School of Engineering


Science & Technology

Electrical & Systems Engineering
Speaker Information

Changqing Wang
PhD Candidate
Washington Univeristy in St. Louis 

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