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Wednesday, May 16, 2012
1:00 PM - 2:30 PM
CNLS Conference Room (TA-3, Bldg 1690)


Molecules as quantum processors: Quantum process tomography as a tool for unraveling quantum coherent effects in photosynthesis.

Alan Aspuru-Guzik
Department of Chemistry and Chemical Biology, Harvard University

Observed long-lived coherences in various photosynthetic complexes a at cryogenic and room temperature have generated vigorous efforts both in theory and experiment to understand their origins and explore their potential role to 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?, and second: Why is the coherence preserved for these 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 experments (quantum process tomography, QPT) to extract the model-independent dynamical information, at the level of the electronic density matrix, about the energy transfer process from combinations of several ultrafast experiments designed to invert this quantum process matrix. This allows us to answer the crucial question of “How much information is in two-dimensional spectra?” and to make the case that QPT is a relevant reformulation of the problem with the goal to maximize the extracted information about the system as a function of the number of experiments carried out. I will describe QPT experiments currently underway.

Host: Sergei Tretiak, T-1: PHYSICS AND CHEMISTRY OF MATERIALS, 667-8351