Title: [Joint CQSE & NCTS Seminar] Quantum Electrodynamical Chemistry: Molecules Coupled with Vacuum Fluctuations of Electromagnetic Fields
Speaker: Dr. Liang-Yan Hsu (Associate Research Fellow, Institute of Atomic and Molecular Sciences, Academia Sinica)
Date: Feb. 18, 2022, 14:30-15:30
Place: Rm. 307, Chee-Chun Leung Cosmology Hall 3F, NTU

Abstract:
In this talk, I will briefly introduce an emerging field “QED chemistry” and my
latest development in this research direction. In the past two years, control of chemical
processes by a vacuum electromagnetic field has received considerable attention
because the entry of quantum electrodynamics into chemistry is a wholly new concept
and a huge breakthrough in basic science. Quantum light can affect molecules in a
variety of aspects, and I will focus on molecular fluorescence coupled with plasmon
polaritons or cavity photons. In the framework of macroscopic quantum
electrodynamics, I developed a unified theory of molecular fluorescence, which allows
us to describe the dynamics of molecular fluorescence coupled to quantum light from
weak to strong light-matter couplings (from Franck-Condon to polariton regimes) in a
complicated dielectric environment. Based on this theory, we showed an interesting
phenomenon called Franck-Condon-Rabi oscillation, and derived a parameter-free
formula which can be used to estimate the exciton-polariton coupling for single
molecules in a nanocavity. Our theory is in good agreement with the reported
experimental results [Chikkaraddy et al., Nature 535, 127-130 (2016)]. In addition, we
investigated the coherent-to-incoherent transition of molecular fluorescence of a
chromophore above a silver surface (including bulk and thin-film systems) and explored
the distance dependence of fluorescence rate enhancement. Moreover, in the presence of
arbitrary inhomogeneous, dispersive, and absorbing media, we established a generalized
theory of molecular emission power spectrum which can be expressed as the product of
the lineshape function and electromagnetic environment factor (EEF). Our study clearly
shows that molecular emission power spectra cannot be simply interpreted by the

lineshape function (quantum dynamics of a molecular emitter), and the effect of the
EEFs (photon propagation in a dielectric environment) has to be carefully considered.

Biography Brief:
Education
‧ B.S., Chemistry, 2005, National Taiwan University, Taiwan
‧ M.S., Chemistry, 2008, National Taiwan University, Taiwan
‧ Ph.D., Chemistry 2015, Princeton University, USA
Experience
‧ Postdoctoral Fellow, Princeton University, USA (2015-2016)
‧ Postdoctoral Fellow, Northwestern University, USA (2016-2017)
‧ Assistant Research Fellow, Institute of Atomic and Molecular Sciences,
Academia Sinica, Taiwan (2017-2021)
‧ Associate Research Fellow, Institute of Atomic and Molecular Sciences,
Academia Sinica, Taiwan (2021-Present)
Research Interests
‧ Nanoelectronics (Molecular Electronics)
‧ Methodology of Quantum Transport Theory at the Nanoscale (Electron, Exciton,
Heat, and Spin Transport)
‧ Light-Matter Interactions at the Nanoscale (Plasmon-Coupled Exciton Transfer
and Spectroscopy)
‧ Polariton Chemistry (Applications of Macroscopic Quantum Electrodynamics in
Chemistry)