59,686 research outputs found
Enhancement of vortex pinning in superconductor/ferromagnet bilayers via angled demagnetization
We use local and global magnetometry measurements to study the influence of
magnetic domain width w on the domain-induced vortex pinning in
superconducting/ferromagnetic bilayers, built of a Nb film and a ferromagnetic
Co/Pt multilayer with perpendicular magnetic anisotropy, with an insulating
layer to eliminate proximity effect. The quasi-periodic domain patterns with
different and systematically adjustable width w, as acquired by a special
demagnetization procedure, exert tunable vortex pinning on a superconducting
layer. The largest enhancement of vortex pinning, by a factor of more than 10,
occurs when w ~ 310 nm is close to the magnetic penetration depth.Comment: 5 pages, 3 figures, accepted to Phys. Rev. B, Rapid Communication
Probing non-Abelian statistics of Majorana fermions in ultracold atomic superfluid
We propose an experiment to directly probe the non-Abelian statistics of
Majorana fermions by braiding them in an s-wave superfluid of ultracold atoms.
We show different orders of braiding operations give orthogonal output states
that can be distinguished through Raman spectroscopy. Realization of Majorana
bound states in an s-wave superfluid requires strong spin-orbital coupling and
a controllable Zeeman field in the perpendicular direction. We present a simple
laser configuration to generate the artificial spin-orbital coupling and the
required Zeeman field in the dark state subspace.Comment: 4 pages; Add detailed discussion of feasibility of the scheme;add
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Topological Bose-Mott Insulators in a One-Dimensional Optical Superlattice
We study topological properties of the Bose-Hubbard model with repulsive
interactions in a one-dimensional optical superlattice. We find that the Mott
insulator states of the single-component (two-component) Bose-Hubbard model
under fractional fillings are topological insulators characterized by a nonzero
charge (or spin) Chern number with nontrivial edge states. For ultracold atomic
experiments, we show that the topological Chern number can be detected through
measuring the density profiles of the bosonic atoms in a harmonic trap.Comment: 5 pages, published versio
Implementation of universal quantum gates based on nonadiabatic geometric phases
We propose an experimentally feasible scheme to achieve quantum computation
based on nonadiabatic geometric phase shifts, in which a cyclic geometric phase
is used to realize a set of universal quantum gates. Physical implementation of
this set of gates is designed for Josephson junctions and for NMR systems.
Interestingly, we find that the nonadiabatic phase shift may be independent of
the operation time under appropriate controllable conditions. A remarkable
feature of the present nonadiabatic geometric gates is that there is no
intrinsic limitation on the operation time, unlike adiabatic geometric gates.
Besides fundamental interest, our results may simplify the implementation of
geometric quantum computation based on solid state systems, where the
decoherence time may be very short.Comment: 5 pages, 2 figures; the version published in Phys. Rev. Let
Performance analysis of full bridge, boost half bridge and half bridge topologies for application in phase shift converters
In this paper, performances of three topologies of bidirectional ports applicable to phase shift converters are compared. The proposed topologies include full bridge, half bridge and boost-half bridge that are commonly used as bi-directional port in various topologies of DC converters. The proposed analyses based on several indicators and characteristics of the topologies including reliability factor, switching loss, current ripple, cost, size, efficiency, range of power flow versus phase shift angle and control complexity. A phase shift converter based on proposed topologies was simulated using P-SIM. The analysis shows that considering all effective factors, full bridge topology provides better characteristics compared with others and can be selected for a phase shift converter. Also in some applications other topologies still remain a favorite choice. © 2013 IEEE
Implementation of quantum gates based on geometric phases accumulated in the eigenstates of periodic invariant operators
We propose a new strategy to physically implement a universal set of quantum
gates based on geometric phases accumulated in the nondegenerate eigenstates of
a designated invariant operator in a periodic physical system. The system is
driven to evolve in such a way that the dynamical phase shifts of the invariant
operator eigenstates are the same (or {\it mod} ) while the corresponding
geometric phases are nontrivial.
We illustrate how this strategy to work in a simple but typical NMR-type
qubit system.Comment: 4 page
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