Quantum Hall fluids in the presence of topological defects

Abstract

We review our recent results on the physics of quantum Hall fluids at Jain and non conventional fillings within a general field theoretic framework. We focus on a peculiar conformal field theory (CFT), the one obtained by means of the m-reduction technique, and stress its power in describing strongly correlated low dimensional condensed matter systems in the presence of localized impurities or topological defects. By exploiting the notion of Morita equivalence for field theories on noncommutative two-tori and choosing rational values of the noncommutativity parameter, we find a general one-to-one correspondence between the m-reduced conformal field theory describing the quantum Hall fluid and an Abelian noncommutative field theory. As an example of application of the formalism, we study a quantum Hall bilayer at nonconventional fillings in the presence of a localized topological defect and briefly recall its boundary state structure corresponding to two different boundary conditions, the periodic as well as the twisted boundary conditions respectively, which give rise to different topological sectors on a torus. Then we introduce generalized magnetic translation operators as tensor products, which act on the quantum Hall fluid and defect space respectively, and compute their action on the boundary partition functions: in this way their role as boundary condition changing operators is fully evidenced. From such results we infer the general structure of generalized magnetic translations in our model and clarify the deep relation between noncommutativity and non-Abelian statistics of quasi-hole excitations, which is crucial for physical implementations of topological quantum computing.