Berlin 2012 – wissenschaftliches Programm

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AGPhil: Arbeitsgruppe Philosophie der Physik

AGPhil 3: Complex and Open Systems

AGPhil 3.1: Hauptvortrag

Dienstag, 27. März 2012, 09:30–10:15, H 2033

Open Quantum Systems: Where is the system and where is the reservoir ? — •Joachim Ankerhold — Institut für Theoretische Physik, Universität Ulm

The conventional treatment of open quantum systems, as they appear e.g. in condensed phase structures, starts from a separation between a subunit, which contains a smaller number of interesting degrees of freedom and is termed the 'system', and a much larger subunit, termed the bath or 'reservoir', which in many cases carries a macroscopically large number of degrees of freedom. These so-called 'system+reservoir' models have been very successfully applied in various fields in physics to describe decoherence and relaxation processes. Accordingly, one considers the reduced density operator of the system and derives for the time evolution e.g. approximate reduced equations of motion or formally exact expressions in terms of path integrals. Beyond the regime of very weak system-reservoir interaction (typical for quantum optical systems), however, an understanding of reduced system properties becomes often a non-trivial matter. In this talk, I will discuss some examples to shed light on the limitations of our naive picture, namely, the failure of classical concepts for certain observables, the existence of coherent reduced dynamics only due to a reservoir, and the appearance of a classical reduced system in the deep quantum domain.