Nonequilibrium Energy Transport in Nanostructures

• Applicant: Professor Dr. Peter Nalbach
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Theoretical Condensed Matter Physics
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 253320334

As electronic devices and sensory equipment continuously become smaller following Moore's law several new challenges emerge. On the one hand quantum effects become dominant and have to be included into the design of nanocircuitry. In addition, however, dumped excess energy due to inevitable Ohmic losses has actively to be routed out of the nanocircuit since passive heat sinking fails at the nanoscale. Active control of nonequilibrium quantum energy transport through nanosystems is widely unexplored due to a lack of adequate theoretical tools. Quantum energy transfer, at the same time, is of tremendous relevance for natural light-harvesting in photosynthesis which basically fuels live on earth. Photosynthesis starts with the absorption of light in biomolecular antennae complexes. An exciton is formed which is then transferred from the antenna to a reaction center (RC). There, chemical energy storage is initiated by charge separation of the exciton. It is a long standing puzzle how nature ensures a quantum yield of almost 100 % for the energy transfer to the RC. Growing evidence indicates that long-lived quantum coherence is beneficial. Long enough life times result from correlations in the environmental fluctuations due to their strong non-Markovian character. A full analysis is missing since different fluctuations couple via non-commuting operators to the excitons (site and coupling energy fluctuations). This results in strongly correlated dynamics for whose treatment we lack adequate theoretical methods.Our aim is the development of a novel numerical method for nonequilibrium quantum transport of energy through molecular entities and nanoelectronic devices. It allows to describe driven quantum systems in contact with several bosonic energy reservoirs at different temperatures. Reservoirs with arbitrary fluctuation spectra coupling via non-commuting operators to the system will be treatable. The proposed method is an extension of the well known equilibrium quasi adiabatic path integral approach. It is based on an iterative scheme which allows to calculate experimentally accessible observables as energy current in a numerically exact manner. With the new method we will clarify then the influence of correlations between site and coupling energy fluctuations on coherence life times and, more importantly, on natures superior energy transfer efficiency in hotosynthetic complexes. Furthermore, we will determine how to control actively and efficiently quantum energy transport in nanodevices in order to facilitate heat sinking of Ohmic losses in nano or molecular electronics. To this end we investigate the extension of the dissipative Landau Zener problem to nonequilibrium and quantum control of energy transport by applying laser pulses. In total, our method will allow to study, understand and optimize quantum energy transport and its active control in natural and artificial nanostructures.

• DFG Programme: Research Grants