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Online Seminar: Quantum photonics for nano-scaled molecules: Novel spectroscopic probes for exciton and phonon dynamics using quantum light

ABSTRACT

Conventional multidimensional spectroscopy uses classical light to detect matter properties through varying its response with frequencies or time delays. Quantum nature of light opens up new avenues for spectroscopy by utilizing parameters of the quantum state of light as novel control knobs and through the variation of photon statistics by coupling to matter. Elaborate experiments have demonstrated the state-of-the-art technology for generating quantum light source by means of entanglement and squeezing. The spectroscopy, however, is just a beginning field along this line. In this talk I will thoroughly explain our recent work on quantum light nonlinear spectroscopy, which may bring us new knowledge on nano-scaled molecules. The main theme will cover three related topics: (I) Two-dimensional coherent spectroscopy for the cooperative dynamics of cavity polaritons when the molecules are interacting with nanostructures; (II) Multidimensional quantum light probe for nonradiative relaxation of molecules; (III) Quantum cooperativity and condensate of phonons driven far from equilibrium. I will start from a brief introduction of multidimensional spectroscopy, including the basic concepts and terminologies. I will first show the time- and frequency-resolved spectroscopy for cavity polaritons to monitor the cooperative motion of molecules against the local fluctuations (disorder). The molecular transitions are resonant with the photon modes in confined geometry, which results in the joint matter-photon states, known as polaritons. Secondly, I will talk about the multidimensional spectroscopic probes, using coincidence counting of multiple photons. This technique will be further developed for molecules coupled to nanostructure, associated with the application to photosynthetic antenna. This spectroscopy provides a versatile tool for controlling the relaxation pathways and rates. Thirdly, I will discuss the quantum coherence and cooperativity in THz phonons in molecules driven far from equilibrium. This leads to out-of-equilibrium phonon condensate and a full quantum theory of such condensate will be presented. We predicted the nonequilibrium phase transition through the phonon statistics and the spectroscopic feature to observe the condensate in future experiments. The talk will also cover an outlook for the quantum nonlinear spectroscopy for nanomaterials.
 

BIOGRAPHY

Dr Zhedong Zhang received his Ph.D. in physics from State University of New York in 2016, supervised by Prof. Jin Wang and Prof. Maxim Olshanii. After the graduation, he moved to University of California Irvine to work as postdoctoral scholar with Prof. Shaul Mukamel, on nonlinear optical spectroscopy of nano-scaled molecules. Later he joined the Institute for Quantum Science and Engineering at Texas A&M University to work with Prof. Marlan Scully and Prof. Girish Agarwal on quantum thermodynamics and quantum nonlinear spectroscopy. He obtained the Robert A. Welch Postdoctoral Fellowship since 2019.

Dr Zhang’s research interest mainly focuses on two fields: (1) nonlinear optical spectroscopy and (2) quantum thermodynamics for nanomaterials. The first one is to develop the time- and spatial-resolved nonlinear spectroscopies (e.g., using X-ray and quantum properties of light) to monitor the dynamical information of complex molecules and novel materials. The second one is aiming at the nonequilibrium thermodynamic processes of mesoscopic systems with long-range quantum coherence/entanglement. He has over 20 professional publications on high-profile journals, including Phys. Rev. Lett., J. Phys. Chem. Lett., Phys. Rev. A, Phys. Rev. B and so on.
 

Please register via :

https://cityu.zoom.us/meeting/register/tJEocemgqz8vHdCGeSVtirueo6KlurIT7ypj

 

Event Details
Speaker
Dr Zhang Zhedong
Postdoctoral Research Associate, Institute for Quantum Science and Engineering, Texas A&M University

Date & Time
20 April 2020 10:00 am

Venue
Zoom Meeting, City University of Hong Kong

Chair
Dr LI Xiao (34427311 xiao.li@cityu.edu.hk)