Adele Naddeo

Twisted CFT and bilayer quantum Hall systems in the presence of an impurity

Abstract We identify the impurity interactions of the recently proposed CFT description of a bilayer quantum Hall system at filling ν= m pm+2 [Mod. Phys. Lett. A 15 (2000) 1679]. Such a CFT is obtained by m -reduction on the one layer system, with a resulting pairing symmetry and presence of quasi-holes. For the m =2 case boundary terms are shown to describe an impurity interaction which allows for a localized tunnel of the Kondo problem type. The presence of an anomalous fixed point is evidenced at finite coupling which is unstable with respect to unbalance and flows to a vacuum state with no quasi-holes.

A conformal field theory description of magnetic flux fractionalization in Josephson junction ladders

Abstract.We show how the recently proposed effective theory for a Quantum Hall systemnat “paired states” filling ν=1xa0[1,2], the twisted model (TM), well adapts to describe thenphenomenology of Josephson Junction ladders (JJL) in the presence of defects. In particular it is shown how naturally the phenomenon of flux fractionalization takes place in such a description and its relation with the discrete symmetries present in the TM. Furthermore we focus onn“closed” geometries, which enable us to analyze the topological properties of the ground state of the system in relation to the presence of half flux quanta. nn

A twisted conformal field theory description of dissipative quantum mechanics

Abstract We show how the recently proposed CFT for a bilayer quantum Hall system at filling ν= m pm+2 [Mod. Phys. Lett. A 15 (2000) 1679; Nucl. Phys. B 641 (2002) 547; Phys. Lett. B 571 (2003) 250], the twisted model (TM), is equivalent to the system of two massless scalar bosons with a magnetic boundary interaction as introduced in [Nucl. Phys. B 443 (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.

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.

CFT description of the fully frustrated XY model and phase diagram analysis

Following an earlier suggestion, we show how the symmetry of the fully frustrated XY (FFXY) model on a square lattice can be accounted for in the framework of the m-reduction procedure developed for a Quantum Hall system at paired states fillings ν = 1. The resulting twisted conformal field theory (CFT) with central charge c = 2 is shown to well describe the physical properties of the FFXY model. In particular, the whole phase diagram is recovered by analysing the flow from the Z2 degenerate vacuum of the c = 2 CFT to the infrared fixed point unique vacuum of the CFT. The last theory is known to successfully describe the critical behaviour of the system at the overlap temperature for the Ising and vortex-unbinding transitions.

SU(N) multi-Skyrmions at finite volume

We study multi-soliton solutions of the four-dimensional SU(N) Skyrme model by combining the hedgehog ansatz for SU(N) based on the harmonic maps of

Fully frustrated Josephson junction ladders with Mobius boundary conditions as topologically protected qubits

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QUANTUM PHASE EXCITATIONS IN GINZBURG–LANDAU SUPERCONDUCTORS

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