5,731 research outputs found
Universal pulse sequence to minimize spin dephasing in the central spin decoherence problem
We present a remarkable finding that a recently discovered [G. S. Uhrig,
Phys. Rev. Lett. 98, 100504 (2007)] series of pulse sequences, designed to
optimally restore coherence to a qubit in the spin-boson model of decoherence,
is in fact completely model-independent and generically valid for arbitrary
dephasing Hamiltonians given sufficiently short delay times between pulses. The
series maximizes qubit fidelity versus number of applied pulses for
sufficiently short delay times because the series, with each additional pulse,
cancels successive orders of a time expansion for the fidelity decay. The
"magical" universality of this property, which was not appreciated earlier,
requires that a linearly growing set of "unknowns" (the delay times) must
simultaneously satisfy an exponentially growing set of nonlinear equations that
involve arbitrary dephasing Hamiltonian operators.Comment: Published in PRL, revise
Intraindustry Trade and the Environment: Is There a Selection Effect?
Replaced with revised version of paper 08/06/10.Environment, Trade, Monopolistic Competition, Selection effect, Environmental quality, Panel data, OECD, Pollution, Environmental Economics and Policy, International Development, International Relations/Trade, Q56, Q51, Q53, Q58, F12, F18,
Gis Based Inventory of the Rivers of Northeastern Region of India For Their Conservation and Management
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
A number conserving theory for topologically protected degeneracy in one-dimensional fermions
Semiconducting nanowires in proximity to superconductors are among promising
candidates to search for Majorana fermions and topologically protected
degeneracies which may ultimately be used as building blocks for topological
quantum computers. The prediction of neutral Majorana fermions in the
proximity-induced superconducting systems ignores number-conservation and thus
leaves open the conceptual question of how a topological degeneracy that is
robust to all local perturbations arises in a number-conserving system. In this
work, we study how local attractive interactions generate a topological
ground-state near-degeneracy in a quasi one-dimensional superfluid using
bosonization of the fermions. The local attractive interactions opens a
topological quasiparticle gap in the odd channel wires (with more than one
channel) with end Majorana modes associated with a topological near-degeneracy.
We explicitly study the robustness of the topological degeneracy to local
perturbations and find that such local perturbations result in quantum phase
slips which split of the topological degeneracy by an amount that does not
decrease exponentially with the length of the wire, but still decreases rapidly
if the number of channels is large. Therefore a bulk superconductor with a
large number of channels is crucial for true topological degeneracy.Comment: 11 pages, 2 figure
Magnetic field-assisted manipulation and entanglement of Si spin qubits
Architectures of donor-electron based qubits in silicon near an oxide
interface are considered theoretically. We find that the precondition for
reliable logic and read-out operations, namely the individual identification of
each donor-bound electron near the interface, may be accomplished by
fine-tuning electric and magnetic fields, both applied perpendicularly to the
interface. We argue that such magnetic fields may also be valuable in
controlling two-qubit entanglement via donor electron pairs near the interface.Comment: 4 pages, 4 figures. 1 ref and 1 footnote adde
Localization in one-dimensional incommensurate lattices beyond the Aubry-Andr\'e model
Localization properties of particles in one-dimensional incommensurate
lattices without interaction are investigated with models beyond the
tight-binding Aubry-Andr\'e (AA) model. Based on a tight-binding t_1 - t_2
model with finite next-nearest-neighbor hopping t_2, we find the localization
properties qualitatively different from those of the AA model, signaled by the
appearance of mobility edges. We then further go beyond the tight-binding
assumption and directly study the system based on the more fundamental
single-particle Schr\"odinger equation. With this approach, we also observe the
presence of mobility edges and localization properties dependent on
incommensuration.Comment: 5 pages, 6 figure
- …