Browsing by Author "Henrich, Markus"

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Local aspects of modular quantum systems in nonequilibrium
(2007) Henrich, Markus; Mahler, Günter (Prof. Dr.)
Thermodynamics and statistic physics developed as one of the most fruitful physical concepts. Seen from the scientific point of view their range of application extends over far areas, not only in physics. The progressive nano-technology makes it necessary, the applicability for that already admitted concepts from classical thermodynamics on the microscopic level to examine. Questions about the extensivity of the energy and entropy, as well as about the existence of a temperature are just as important as the investigation of thermodynamic cyclic processes for quantum systems. With the help of the theory of open quantum systems stationary nonequilibrium states are simulated. If the quantum system under consideration is not driven heat transport can be examined. The question about local characteristics of individual subsystems is inherent. Because only if the local change of energy of a subsystem is known, a local heat or energy current can be determined. The interaction between the subsystems is for the characterisation of the energy transfer of crucial importance. A quantum-mechanical analysis shows, that by the choice of the measuring basis in an experiment specifies variables such as work and heat. For driven quantum systems in nonequilibrium it shows up that from classical thermodynamics admitted cyclic processes are realizable. The simplest quantum system, a spin can undergo, e.g., an Otto-cycle if suitable embedded and operates thus as heat pump or heat engine. The work mode depends on the local energy splitting as well as on the temperature gradient.