Interference and Interaction in Multiwall Carbon Nanotubes

We report equilibrium electric resistance R and tunneling spectroscopy dI/dV measurements obtained on single multiwall nanotubes contacted by four metallic Au fingers from above. At low temperature quantum interference phenomena dominate the magnetoresistance. The phase-coherence and elastic-scattering lengths are deduced. Because the latter is of order of the circumference of the nanotubes, transport is quasi-ballistic. This result is supported by a dI/dV spectrum which is in good agreement with the density-of-states (DOS) due to the one-dimensional subbands expected for a perfect single-wall tube. As a function of temperature T the resistance increases on decreasing T and saturates at approx. 1-10 K for all measured nanotubes. R(T) cannot be related to the energy-dependent DOS of graphene but is mainly caused by interaction and interference effects. On a relatively small voltage scale of order 10 meV, a pseudogap is observed in dI/dV which agrees with Luttinger-Liquid theories for nanotubes. Because we have used quantum diffusion based on Fermi-Liquid as well as Luttinger-Liquid theory in trying to understand our results, a large fraction of this paper is devoted to a careful discussion of all our results.Comment: 14 pages (twocolumn), 8 figure

Interference in transport through double barriers in interacting quantum wires

We investigate interference effects of the backscattering current through a double-barrier structure in an interacting quantum wire attached to noninteracting leads. Depending on the interaction strength and the location of the barriers, the backscattering current exhibits different oscillation and scaling characteristics with the applied voltage in the strong and weak interaction cases. However, in both cases, the oscillation behaviors of the backscattering current are mainly determined by the quantum mechanical interference due to the existence of the double barriers.Comment: 6 pages, 3 fig

Using atomic interference to probe atom-surface interaction

We show that atomic interference in the reflection from two suitably polarized evanescent waves is sensitive to retardation effects in the atom-surface interaction for specific experimental parameters. We study the limit of short and long atomic de Broglie wavelength. The former case is analyzed in the semiclassical approximation (Landau-Zener model). The latter represents a quantum regime and is analyzed by solving numerically the associated coupled Schroedinger equations. We consider a specific experimental scheme and show the results for rubidium (short wavelength) and the much lighter meta-stable helium atom (long wavelength). The merits of each case are then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX sourc

Role of interference in quantum state transfer through spin chains

We examine the role that interference plays in quantum state transfer through several types of finite spin chains, including chains with isotropic Heisenberg interaction between nearest neighbors, chains with reduced coupling constants to the spins at the end of the chain, and chains with anisotropic coupling constants. We evaluate quantitatively both the interference corresponding to the propagation of the entire chain, and the interference in the effective propagation of the first and last spins only, treating the rest of the chain as black box. We show that perfect quantum state transfer is possible without quantum interference, and provide evidence that the spin chains examined realize interference-free quantum state transfer to a good approximation.Comment: 10 figure

Spin wave vortex from the scattering on Bloch point solitons

The interaction of a spin wave with a stationary Bloch point is studied. The topological non-trivial structure of the Bloch point manifests in the propagation of spin waves endowing them with a gauge potential that resembles the one associated with the interaction of a magnetic monopole and an electron. By pursuing this analogy, we are led to the conclusion that the scattering of spin waves and Bloch points is accompanied by the creation of a magnon vortex. Interference between such a vortex and a plane wave leads to dislocations in the interference pattern that can be measurable by means of magnon holography

Coherent backscattering of Bose-Einstein condensates in two-dimensional disorder potentials

We study quantum transport of an interacting Bose-Einstein condensate in a two-dimensional disorder potential. In the limit of vanishing atom-atom interaction, a sharp cone in the angle-resolved density of the scattered matter wave is observed, arising from constructive interference between amplitudes propagating along reversed scattering paths. Weak interaction transforms this coherent backscattering peak into a pronounced dip, indicating destructive instead of constructive interference. We reproduce this result, obtained from the numerical integration of the Gross-Pitaevskii equation, by a diagrammatic theory of weak localization in presence of a nonlinearity.Comment: 4 pages, 4 figure