Fermion confinement via Quantum Walks in 2D+1 and 3D+1 spacetime

We analyze the properties of a two and three dimensional quantum walk that are inspired by the idea of a brane-world model put forward by Rubakov and Shaposhnikov [1]. In that model, particles are dynamically confined on the brane due to the interaction with a scalar field. We translated this model into an alternate quantum walk with a coin that depends on the external field, with a dependence which mimics a domain wall solution. As in the original model, fermions (in our case, the walker), become localized in one of the dimensions, not from the action of a random noise on the lattice (as in the case of Anderson localization), but from a regular dependence in space. On the other hand, the resulting quantum walk can move freely along the "ordinary" dimension.Comment: 5 pages, 6 figure

Coherent macroscopic quantum tunneling in boson-fermion mixtures

We show that the cold atom systems of simultaneously trapped Bose-Einstein condensates (BEC's) and quantum degenerate fermionic atoms provide promising laboratories for the study of macroscopic quantum tunneling. Our theoretical studies reveal that the spatial extent of a small trapped BEC immersed in a Fermi sea can tunnel and coherently oscillate between the values of the separated and mixed configurations (the phases of the phase separation transition of BEC-fermion systems). We evaluate the period, amplitude and dissipation rate for $^{23}$Na and $^{40}$K-atoms and we discuss the experimental prospects for observing this phenomenon.Comment: 4 pages, 3 figure

The spread of the gluon k_t-distribution and the determination of the saturation scale at hadron colliders in resummed NLL BFKL

The transverse momentum distribution of soft hadrons and jets that accompany central hard-scattering production at hadron colliders is of great importance, since it has a direct bearing on the ability to separate new physics signals from Standard Model backgrounds. We compare the predictions for the gluonic k_t-distribution using two different approaches: resummed NLL BFKL and DGLAP evolution. We find that as long as the initial and final virtualities (k_t) along the emission chain are not too close to each other, the NLL resummed BFKL results do not differ significantly from those obtained using standard DGLAP evolution. The saturation momentum Q_s(x), calculated within the resummed BFKL approach, grows with 1/x even slower than in the leading-order DGLAP case.Comment: 24 pages, 8 figures, An improved, slightly more precise NLL resummation is used and the figures are updated accordingly. The conclusions are unchange

Nanomechanical effects in an Andreev quantum dot

We consider a quantum dot with mechanical degrees of freedom which is coupled to superconducting electrodes. A Josephson current is generated by applying a phase difference. In the absence of coupling to vibrations, this setup was previously proposed as a detector of magnetic flux and we wish here to address the effect of the phonon coupling to this detection scheme. We compute the charge on the quantum dot and determine its dependence on the phase difference in the presence of phonon coupling and Coulomb interaction. This allows to identify regions in parameter space with the highest charge to phase sensitivity, which are relevant for flux detection. Further insight about the interplay of such couplings and subsequent entanglement properties between electron and phonon degrees of freedom are gained by computing the von Neuman entropy.Comment: 9 pages, 7 figures; minor corretion

Marginal topological properties of graphene: a comparison with topological insulators

The electronic structures of graphene systems and topological insulators have closely-related features, such as quantized Berry phase and zero-energy edge states. The reason for these analogies is that in both systems there are two relevant orbital bands, which generate the pseudo-spin degree of freedom, and, less obviously, there is a correspondence between the valley degree of freedom in graphene and electron spin in topological insulators. Despite the similarities, there are also several important distinctions, both for the bulk topological properties and for their implications for the edge states -- primarily due to the fundamental difference between valley and spin. In view of their peculiar band structure features, gapped graphene systems should be properly characterized as marginal topological insulators, distinct from either the trivial insulators or the true topological insulators.Comment: This manuscript will be published on the Proceedings of the 2010 Nobel Symposium on Graphene and Quantum Matte

Spin-density induced by electromagnetic wave in two-dimensional electron gas

We consider the magnetic response of a two-dimensional electron gas (2DEG) with a spin-orbit interaction to a long-wave-length electromagnetic excitation. We observe that the transverse electric field creates spin polarization perpendicular to the 2DEG plane. The effect is more prominent in clean systems with resolved spin-orbit-split subbands, and reaches maximum when the frequency of the wave matches the subband splitting at the Fermi momentum. The relation of this effect to the spin-Hall effect is discussed.Comment: Final published for

Fuzzy Fluid Mechanics in Three Dimensions

We introduce a rotation invariant short distance cut-off in the theory of an ideal fluid in three space dimensions, by requiring momenta to take values in a sphere. This leads to an algebra of functions in position space is non-commutative. Nevertheless it is possible to find appropriate analogues of the Euler equations of an ideal fluid. The system still has a hamiltonian structure. It is hoped that this will be useful in the study of possible singularities in the evolution of Euler (or Navier-Stokes) equations in three dimensions.Comment: Additional reference

Tunneling Spectroscopy of Two-level Systems Inside Josephson Junction

We consider a two-level (TL) system with energy level separation Omega_0 inside a Josephson junction. The junction is shunted by a resistor R and is current I (or voltage V = RI) biased. If the TL system modulates the Josephson energy and/or is optically active, it is Rabi driven by the Josephson oscillations in the running phase regime near the resonance 2eV = Omega_0. The Rabi oscillations, in turn, translate into oscillations of current and voltage which can be detected in noise measurements. This effect provides an option to fully characterize the TL systems and to find the TL's contribution to the decoherence when the junction is used as a qubit.Comment: 4 page

Topological confinement in bilayer graphene

We study a new type of one-dimensional chiral states that can be created in bilayer graphene (BLG) by electrostatic lateral confinement. These states appear on the domain walls separating insulating regions experiencing the opposite gating polarity. While the states are similar to conventional solitonic zero-modes, their properties are defined by the unusual chiral BLG quasiparticles, from which they derive. The number of zero-mode branches is fixed by the topological vacuum charge of the insulating BLG state. We discuss how these chiral states can manifest experimentally, and emphasize their relevance for valleytronics.Comment: 4 pages, 3 figure