Chemical Physics Seminar

Observed long-lived coherences in various photosynthetic complexes at cryogenic and room temperatures have generated vigorous efforts both in theory and experiment to understand their origins and explore their potential role in biological function. The ultrafast signals resulting from the experiments that show evidence for these coherences result from many contributions to the monitored polarization. These experiments raise the following specific questions: what is the role of quantum coherence, if any, in the energy transfer process of these systems? Second, why is the coherence preserved for such long times? In this talk, I will describe our recent efforts to address these two questions using tools from physical chemistry and quantum information theory. We employ and develop several techniques ranging from quantum master equations to explicit atomistic simulations and introduce measures of efficiency, partitioning of contributions to quantum transport, and non-Markovianity in these systems. We propose a new set of ultrafast experiments (quantum process tomography, QPT) to extract model-independent dynamical information regarding the energy transfer process at the level of the electronic density matrix from combinations of several ultrafast experiments designed to invert this quantum process matrix. This not only allows us to answer the crucial question of How much information is in two-dimensional spectra? but also makes the case that QPT is a relevant reformulation of the problem with the goal of maximizing the extracted information about the system as a function of the number of experiments carried out. I will describe QPT experiments currently underway and will conclude by describing our efforts to engineer novel materials for light harvesting and charge transport in organic photovoltaics, and our recent prediction and synthesis of the second largest hole-mobility organic material known using some of the tools mentioned above.