Description of the Problem

The quantized radiation within an optical cavity (e.g. two parallel mirrors) can be strongly coupled to a molecular systems. The radiation-molecule interaction within such optical cavities strongly modifies the potential energy landscape and leads to new  chemical reactivities which has been experimentally realized. Direct quantum dynamics simulations are needed to be performed and convenient new theoretical frameworks are needed to be developed to  understand the mechanistic principles behind these new phenomena.

Theoretical Investigation of Polariton Chemistry

Through direct path-integral based quantum dynamics simulations, we have demonstrated that quantum light-matter interactions can be exploited to tune an isomerization reaction, enhance photo-dissociation or modify photoinduced electron transfer kinetics. In particular one can modify radiation mode frequency (cavity photon frequency) and light-matter coupling strength and use them as control knobs for tuning chemical reactions. Further,  we have demonstrated that when multiple molecules are coupled to a single photon mode, they form a hybrid light-matter super-molecule, which can be photoexcited with a single photon to trigger reactions in many molecules at once.  We also showed that multiple photochemical reactions can be enabled through the exchange of virtual photons between molecules inside a cavity. 

Theoretical Frameworks for Molecular QED

We also found that the light-matter Hamiltonians used in quantum optics are inadequate for describing interactions between molecules and the photon field. We discovered that molecular permanent dipoles, can polarize the photon field, leading to non-orthogonality between the photonic Fock states. We showed that such non-orthogonality, a molecular analogue to the dynamical Casimir Effect, can be exploited to convert single molecular excitation to create multiple photons. We also showed that terms like “Dipole Self-Energy” or “Counter Rotating terms” which are often ignored in quantum optics can have measurable effect on electron transfer kinetics  when coupled to a cavity. 

We have also developed convenient theoretical frameworks to describe light-matter interactions, such as the Polarized Fock State representation, that provides computational convenience as well as conceptually intuitive understanding of new phenomena beyond the quantum Rabi model, and have developed a new coulomb-gauge Hamiltonian that resolved gauge ambiguity under finite electronic truncation in molecular cavity quantum electrodynamics.