3,042 research outputs found
Shot Noise of Spin-Decohering Transport in Spin-Orbit Coupled Nanostructures
We generalize the scattering theory of quantum shot noise to include the full
spin-density matrix of electrons injected from a spin-filtering or
ferromagnetic electrode into a quantum-coherent nanostructure governed by
various spin-dependent interactions. This formalism yields the spin-resolved
shot noise power for different experimental measurement setups--with
ferromagnetic source and ferromagnetic or normal drain electrodes--whose
evaluation for the diffusive multichannel quantum wires with the Rashba (SO)
spin-orbit coupling shows how spin decoherence and dephasing lead to
substantial enhancement of charge current fluctuations (characterized by Fano
factors ). However, these processes and the corresponding shot noise
increase are suppressed in narrow wires, so that charge transport experiments
measuring the Fano factor in a
ferromagnet/SO-coupled-wire/paramagnet setup also quantify the degree of
phase-coherence of transported spin--we predict a one-to-one correspondence
between the magnitude of the spin polarization vector and .Comment: 8 pages, 3 figure; enhanced with 2 new figure
Why the Universe Started from a Low Entropy State
We show that the inclusion of backreaction of massive long wavelengths
imposes dynamical constraints on the allowed phase space of initial conditions
for inflation, which results in a superselection rule for the initial
conditions. Only high energy inflation is stable against collapse due to the
gravitational instability of massive perturbations. We present arguments to the
effect that the initial conditions problem {\it cannot} be meaningfully
addressed by thermostatistics as far as the gravitational degrees of freedom
are concerned. Rather, the choice of the initial conditions for the universe in
the phase space and the emergence of an arrow of time have to be treated as a
dynamic selection.Comment: 12 pages, 2 figs. Final version; agrees with accepted version in
Phys. Rev.
Dynamics of Global Entanglement under Decoherence
We investigate the dynamics of global entanglement, the Meyer-Wallach
measure, under decoherence, analytically. We study two important class of
multi-partite entangled states, the Greenberger-Horne-Zeilinger and the W
state. We obtain exact results for various models of system-environment
interactions (decoherence). Our results shows distinctly different scaling
behavior for these initially entangled states indicating a relative robustness
of the W state, consistent with previous studies.Comment: 5 pages and 5 figure
On the precise connection between the GRW master-equation and master-equations for the description of decoherence
We point out that the celebrated GRW master-equation is invariant under
translations, reflecting the homogeneity of space, thus providing a particular
realization of a general class of translation-covariant Markovian
master-equations. Such master-equations are typically used for the description
of decoherence due to momentum transfers between system and environment.
Building on this analogy we show the exact relationship between the GRW
master-equation and decoherence master-equations, further providing a
collisional decoherence model formally equivalent to the GRW master-equation.
This allows for a direct comparison of order of magnitudes of relevant
parameters. This formal analogy should not lead to confusion on the utterly
different spirit of the two research fields, in particular it has to be
stressed that the decoherence approach does not lead to a solution of the
measurement problem. Building on this analogy however the feasibility of the
extension of spontaneous localization models in order to avoid the infinite
energy growth is discussed. Apart from a particular case considered in the
paper, it appears that the amplification mechanism is generally spoiled by such
modifications.Comment: 9 pages, latex, no figures, to appear on J. Phys.
Decoherence and entropy of primordial fluctuations II. The entropy budget
We calculate the entropy of adiabatic perturbations associated with a
truncation of the hierarchy of Green functions at the first non trivial level,
i.e. in a self-consistent Gaussian approximation. We give the equation
governing the entropy growth and discuss its phenomenology. It is parameterized
by two model-dependent kernels. We then examine two particular inflationary
models, one with isocurvature perturbations, the other with corrections due to
loops of matter fields. In the first model the entropy grows rapidely, while in
the second the state remains pure (at one loop).Comment: 28 page
Topologically decoherence-protected qubits with trapped ions
We show that trapped ions can be used to simulate a highly symmetrical
Hamiltonian with eingenstates naturally protected against local sources of
decoherence. This Hamiltonian involves long range coupling between particles
and provides a more efficient protection than nearest neighbor models discussed
in previous works. Our results open the perspective of experimentally realizing
in controlled atomic systems, complex entangled states with decoherence times
up to nine orders of magnitude longer than isolated quantum systems.Comment: 4 page
Quiz Games as a model for Information Hiding
We present a general computation model inspired in the notion of information
hiding in software engineering. This model has the form of a game which we call
quiz game. It allows in a uniform way to prove exponential lower bounds for
several complexity problems of elimination theory.Comment: 46 pages, to appear in Journal of Complexit
A randomised, double-blind, four-way, crossover trial comparing the 24-h FEV₁ profile for once-daily versus twice-daily treatment with olodaterol, a novel long-acting β₂-agonist, in patients with chronic obstructive pulmonary disease
Background: This randomised, double-blind, four-way, crossover, Phase II study compared the 24-h forced expiratory volume in 1 s (FEV1) profile of alternative dosing frequencies of two total daily doses of olodaterol (5 and 10 mu g) in patients with chronic obstructive pulmonary disease (COPD).
Methods: Patients received olodaterol 2 mu g twice daily (BID), 5 mu g BID, 5 mu g once daily (QD) and 10 mu g QD in a randomised sequence over 3-week treatment periods. Co-primary end points were FEV, area under the curve from 0 to 12 h (AUC(0-12)) and area under the curve from 12 to 24 h (AUC(12-24)) responses. Additional lung-function responses, pharmacokinetics and safety were assessed.
Results: 47 patients were treated. All olodaterol doses provided significant increases in FEV, versus baseline (p < 0.001) and FEV, time profiles were nearly identical for olodaterol 5 and 10 mu g QD. Olodaterol 5 pg QD demonstrated improved FEV, AUC(0-12) and similar AUC(12-24) versus 2 mu g BID. Olodaterol 5 mu g QD showed slightly increased FEV, AUC(0-12) but lower AUC(12-24) compared to 5 mu g BID. Bronchodilation over 24 h was similar for olodaterol 5 pg QD and BID. All doses were well tolerated.
Conclusions: Olodaterol 5 pg QD is efficacious in COPD, with a superior bronchodilatory profile compared to 2 mu g BID, which is close to the same total daily dose, and a similar degree of bronchodilation over 24 h compared with double the daily dose (administered as 10 pg QD or 5 mu g BID)
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