Abstract
An optical system with Parity-time (PT) symmetry is one of the most widely studied platforms in probing the intriguing physics of non-Hermitian Hamiltonians. These include various special phenomena related to exceptional points and phase transitions. In constructing such a system, gain and loss are usually balanced. In the first part of this talk, the speaker will discuss the possibility of constructing a passive system, which respects ideal PT-symmetry by exploring metamaterials with both electric and magnetic resonances using a dipolar model. Instead of balancing gain and loss, the speaker balances scattering and absorption loss to have an analogy to construct an effective PT-symmetric Hamiltonian. Based on the dipolar model, the speaker will discuss the experimental realization of a passive PT-symmetric system with a bright and a dark metamaterial atom using a microwave transmission line platform. The speaker will also show a PT-phase transition of coherent perfect absorption. Such a passive metamaterial with PT-phase transition will be useful for designing optical devices with tunable properties. In the second part of this talk, the speaker will extend the discussion of PT-symmetry within an effective medium model. Instead of a dipolar model, by interpreting the constitutive tensor of a metamaterial as an effective Hamiltonian, the speaker will discuss how magnetic response and electric response can be matched in general to have PT-symmetry by defining an effective parity operator.
About the speaker
Prof Jensen Li received his BEng degree in Electrical and Electronic Engineering from the University of Hong Kong in 1998 and his MPhil and PhD degrees in Physics from the Hong Kong University of Science and Technology in 2000 and 2004 respectively. From 2005 to 2007, he worked in Imperial College London, with support from a Croucher Foundation Postdoctoral Fellowship. From 2007 to 2009, he was a Postdoctoral Researcher at the University of California at Berkeley. From 2009 to 2013, he was an Assistant Professor at the City University of Hong Kong. In 2013, he joined University of Birmingham as a Senior Lecturer.
Prof Li is working mainly on photonic crystals and metamaterials. His research revolves around various extraordinary optical and acoustic phenomena given by metamaterials, with prominent examples such as invisibility cloaking and super-resolution imaging. His current interests are on transformation optics, metasurfaces and complex media.
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