A twisted conformal field theory description of dissipative quantum mechanics

We show how the recently proposed CFT for a bilayer Quantum Hall system at filling nu=m/pm+2, the Twisted Model (TM), is equivalent to the system of two massless scalar bosons with a magnetic boundary interaction as introduced in Nucl. Phys. B443 (1995) 444, at the so called magic points. We are then able to describe, within such a framework, the dissipative quantum mechanics of a particle confined to a plane and subject to an external magnetic field normal to it. Such an analogy is further developed in terms of the TM boundary states, by describing the interaction between an impurity with a Hall system.Comment: 13 pages, no figures, Late

New Results on the Phase Diagram of the FFXY Model: A Twisted CFT Approach

The issue of the number, nature and sequence of phase transitions in the fully frustrated XY (FFXY) model is a highly non trivial one due to the complex interplay between its continuous and discrete degrees of freedom. In this contribution we attack such a problem by means of a twisted conformal field theory (CFT) approach and show how it gives rise to the U (1)$\otimes Z_{2}$ symmetry and to the whole spectrum of excitations of the FFXY model.Comment: 7 pages; talk given by G. Niccoli at "Path Integrals - New Trends and Perspectives International Conference", Max-Planck-Institut, Dresden, Germany, September 23 - 28, 200

Transport properties in bilayer Quantum Hall systems in the presence of a topological defect

Following a suggestion given in Phys. Lett. B 571(2003) 621, we show how a bilayer Quantum Hall system at fillings nu =1/p+1 can exhibit a point-like topological defect in its edge state structure. Indeed our CFT theory for such a system, the Twisted Model (TM), gives rise in a natural way to such a feature in the twisted sector. Our results are in agreement with recent experimental findings (Phys. Rev. B 72 (2005) 041305) which evidence the presence of a topological defect in the transport properties of the bilayer system.Comment: 10 pages, 4 figures; talk given by A. Naddeo at "X Training Course in the Physics of Correlated Electron Systems and High-Tc Superconductors, Vietri sul Mare (SA),Italy, 3-14 October 200

Point-like topological defects in bilayer quantum Hall systems

Following a suggestion given in Phys. Lett. B 571 (2003) 250, we show how a bilayer Quantum Hall system at fillings nu =m/pm+2 can exhibit a point-like topological defect in its edge state structure. Indeed our CFT theory for such a system, the Twisted Model (TM), gives rise in a natural way to such a feature in the twisted sector. Our results are in agreement with recent experimental findings (cond-mat/0503478) which evidence the presence of a topological defect in the bilayer system.Comment: 9 pages, 3 figure

Tunnelling Effects in a Brane System and Quantum Hall Physics

We argue that a system of interacting D-branes, generalizing a recent proposal, can be modelled as a Quantum Hall fluid. We show that tachyon condensation in such a system is equivalent to one particle tunnelling. In a conformal field theory effective description, that induces a transition from a theory with central charge c=2 to a theory with c=3/2, with a corresponding symmetry enhancement.Comment: 12 pages, no figures, Latex, some aspects clarified, sect.3 expanded, references adde

Experimental investigation on free surface vortices driven by tangential inlets

Particle Image Velocimetry (PIV) measurements have been carried out in order to analyze the structure of free surface vortices in a promoting geometry with two tangential inlets. Velocity fields associated to the free surface vortex have been obtained at different horizontal planes and Reynolds numbers. Average velocity fields have been calculated and tangential velocity profiles have been compared at different vortex stages and measurement planes. The results show that tangential flow is uniform along the vortex axis and it scales well with the average exit velocity. The tangential velocity profiles, in comparison to the potential behavior, show discrepancies especially at large distances from the vortex axis. Vorticity fields and circulation profiles have been also derived from the measured velocity fields and discussed. The circulation profiles increase along the vortex radius even at large distances from the vortex axis, so that the potential solution is not applicable at all. The comparison of tangential velocity and circulation profiles between promoted and free vortices, the last presented in a previous paper, shows that the tangential motion in a driven vortex is more intense and predominant over the sink effect (radial motion), except very close to the tank bottom, as in a forced configuration (i.e. rotating cylindrical tank)

Dissipative quantum mechanics and Kondo-like impurities on noncommutative two-tori

In a recent paper, by exploiting the notion of Morita equivalence for field theories on noncommutative tori and choosing rational values of the noncommutativity parameter $\theta$ (in appropriate units), a general one-to-one correspondence between the $m$-reduced conformal field theory (CFT) describing a quantum Hall fluid (QHF) at paired states fillings $\nu =\frac{m}{pm+2}$ and an Abelian noncommutative field theory (NCFT) has been established . That allowed us to add new evidence to the relationship between noncommutativity and quantum Hall fluids\cite% {ncmanybody}. On the other hand, the $m$-reduced CFT is equivalent to a system of two massless scalar bosons with a magnetic boundary interaction as introduced by Callan et al., at the so called ``magic''\ points. We are then able to describe, within such a framework, the dissipative quantum mechanics of a particle confined to a plane and subject to an external magnetic field normal to it. Here we develop such a point of view by focusing on the case $m=2$ which corresponds to a quantum Hall bilayer. The key role of a localized impurity which couples the two layers is emphasized and the effect of noncommutativity in terms of generalized magnetic translations (GMT) is fully exploited. As a result, general GMT operators are introduced, in the form of a tensor product, which act on the QHF and defect space respectively, and a comprehensive study of their rich structure is performed.Comment: 18 pages, 1 figure, accepted for publication in International Journal of Modern Physics

Topological order in Josephson junction ladders with Mobius boundary conditions

We propose a CFT description for a closed one-dimensional fully frustrated ladder of quantum Josephson junctions with Mobius boundary conditions, in particular we show how such a system can develop topological order. Such a property is crucial for its implementation as a "protected" solid state qubit.Comment: 14 pages, 3 figures, to appear in JSTA