Effect of an inhomogeneous external magnetic field on a quantum dot quantum computer

We calculate the effect of an inhomogeneous magnetic field, which is invariably present in an experimental environment, on the exchange energy of a double quantum dot artificial molecule, projected to be used as a 2-qubit quantum gate in the proposed quantum dot quantum computer. We use two different theoretical methods to calculate the Hilbert space structure in the presence of the inhomogeneous field: the Heitler-London method which is carried out analytically and the molecular orbital method which is done computationally. Within these approximations we show that the exchange energy J changes slowly when the coupled dots are subject to a magnetic field with a wide range of inhomogeneity, suggesting swap operations can be performed in such an environment as long as quantum error correction is applied to account for the Zeeman term. We also point out the quantum interference nature of this slow variation in exchange.Comment: 12 pages, 4 figures embedded in tex

Emulating Non-Abelian Topological Matter in Cold Atom Optical Lattices

Certain proposed extended Bose-Hubbard models may exhibit topologically ordered ground states with excitations obeying non-Abelian braid statistics. A sufficient tuning of Hubbard parameters could yield excitation braiding rules allowing implementation of a universal set of topologically protected quantum gates. We discuss potential difficulties in realizing a model with a proposed non-Abelian topologically ordered ground state using optical lattices containing bosonic dipoles. Our direct implementation scheme does not realize the necessary anisotropic hopping, anisotropic interactions, and low temperatures

Quantum theory of spectral diffusion induced electron spin decoherence

A quantum cluster expansion method is developed for the problem of localized electron spin decoherence due to dipolar fluctuations of lattice nuclear spins. At the lowest order it provides a microscopic explanation for the Lorentzian diffusion of Hahn echoes without resorting to any phenomenological Markovian assumption. Our numerical results show remarkable agreement with recent electron spin echo experiments in phosphorus doped silicon.Comment: 5 pages, 1 figur

Coulomb-corrected quantum interference in above-threshold ionization: Working towards multi-trajectory electron holography

Using the recently developed Coulomb Quantum Orbit Strong-Field Approximation (CQSFA), we perform a systematic analysis of several features encountered in above-threshold ionization (ATI) photoelectron angle-resolved distributions (PADs), such as side lobes, and intra- and intercycle interference patterns. The latter include not only the well-known intra-cycle rings and the near-threshold fan-shaped structure, but also previously overlooked patterns. We provide a direct account of how the Coulomb potential distorts different types of interfering trajectories and changes the corresponding phase differences, and show that these patterns may be viewed as generalized holographic structures formed by up to three types of trajectories. We also derive analytical interference conditions and estimates valid in the presence or absence of the residual potential, and assess the range of validity of Coulomb-corrected interference conditions provided in the literature.Comment: 17 pages, 11 figures. Some figures have been compressed in order to comply with the arXiv requirement

Criação de ovinos deslanados em área de cerrado do Amapá.

Visando incentivar a ovinocultura no Amapá, a Empresa Brasileira de Pesquisa Agropecuária - EMBRAPA, atraves da sua Unidade de Pesquisa de Ambito Territorial - UEPAT de Macapá, vem desenvolvendo no Campo Experimental do Cerrado, município de Macapá, experimento a fim de avaliar o comportamento produtivo e reprodutivo de ovinos deslanados da raça Santa Ines em pastagem de quicuio da Amazônia (Brachiaria humidicola).bitstream/item/64921/1/AP-1987-criacao-ovinos-deslanados-cerrado-amapa.pd