Nonequilibrium Energy Transport in Nanostructures

随着电子设备和传感设备按照摩尔定律不断变小，一些新的挑战出现了。一方面，量子效应占主导地位，必须纳入纳米电路的设计。此外，由于被动散热在纳米级失效，由于不可避免的欧姆损耗而产生的多余能量必须主动从纳米电路中排出。由于缺乏足够的理论工具，通过纳米系统的非平衡量子能量输运的主动控制广泛未被探索。与此同时，量子能量转移与光合作用中的自然光收集有着巨大的相关性，光合作用基本上是地球上生命的燃料。光合作用始于生物分子天线复合体对光的吸收。激子形成，然后从天线转移到反应中心（RC）。在那里，化学能量储存是由激子的电荷分离引起的。这是一个长期存在的难题，大自然如何确保几乎100%的量子产量的能量转移到RC。越来越多的证据表明，长时间的量子相干是有益的。由于环境波动具有很强的非马尔可夫性，因而产生了足够长的寿命。由于不同的波动通过非交换算子耦合到激子（位和耦合能量波动），因此缺少完整的分析。这导致了强相关动力学的治疗，我们缺乏足够的理论方法。我们的目标是发展一种新的数值方法来研究能量在分子实体和纳米电子器件中的非平衡量子输运。它允许描述在不同温度下与几个玻色子能量库接触的驱动量子系统。具有任意波动谱通过非交换算符耦合到系统的油藏将是可处理的。该方法是对已知的平衡准绝热路径积分方法的推广。它基于一种迭代方案，该方案允许以数值精确的方式计算实验上可观测到的能量电流。利用新方法，我们将阐明位点和耦合能量波动之间的相关性对相干寿命时间的影响，更重要的是，对天然的热能合成配合物中优越的能量转移效率的影响。此外，我们将确定如何主动有效地控制纳米器件中的量子能量输运，以促进纳米或分子电子学中的欧姆损耗的散热。为此，我们研究了利用激光脉冲将耗散朗道齐纳问题推广到非平衡态和能量输运的量子控制。总之，我们的方法将允许研究、理解和优化量子能量输运及其在天然和人工纳米结构中的主动控制。

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.