Frontiers in the quantum theory of energy transfer

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Interatomic and intermolecular energy transfer underpins a broad range of biological processes (e.g. photosynthesis plants) as well as technological devices (e.g. solar cells). It has even been suggested that the high efficiency of energy transfer within plants relies on quantum effects, but this remains controversial. While the basic mechanism of energy transfer has been known and broadly understood for a number of decades, recently progress in (and synthesis between) theoretical, computational and experimental physics has led to an explosion in the range and complexity of energy transfer-like processes that can be studied. These include the prediction and discovery of related phenomena (e.g. interatomic Coulombic decay), new methods of external control with strong electric or magnetic fields, and a progression from considering only two or three atoms or molecules to considering large ensembles. All of these have advances have required the development of novel theoretical approaches. For example, a theory called quantum electrodynamical density functional theory (QEDFT) can bridge the gap between the quantum-optical picture of an atom (an infinitesimal point-like emitter/absorber) and the quantum chemical picture of an atom (a cloud of electrons around a nucleus).The overall goal of this project is to use these techniques and others as appropriate to push the boundaries of the efficiency of energy transfer between atoms and molecules, with applications in solar cells, radiation biology and excitonics (the analogue of electronics but controlling excitations of molecular states instead of the flow of electrons). The latter in particular is a promising route to low-power versions of today's energy-intensive computers. The novelty of the methodology is a unique mix of techniques from quantum optics and quantum chemistry, which will allow us to generate new results for the rate and dynamics of the rate of energy transfer at the intermediate distances not previously considered. The project will also use reformulations of perturbation theory in order to massively simplify analytical calculation of the rates of few-body energy transfer, which will be applied to design and characterisation of excitonic devices such as transistors. The research aligns with the Physical Sciences area of EPSRC's remit, in particular with light matter interaction and optical phenomena. The longer-term applications of the research in increasing and controlling the efficiency of energy transfer may also align with the solar technology area.