| The simplest one-dimensional model for the studying of non-trivial geometrical effects is a ring shaped device which is formed by joining two arms. We explore the possibility to model such a system as a two level system (TLS). Of particular interest is the analysis of quantum stirring, where circulating current is induced in the Fermi sea by integrating a quantum pump into the closed circuit. The induced current may have either the same or the opposite sense with respect to the ``pushing" direction of the pump. We work out explicit expressions for the associated geometric conductance using the Kubo-Dirac monopoles picture and discuss whether the topology is properly reflected within the framework of the TLS modeling. |
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