687 research outputs found
Coulomb-enhanced dynamic localization and Bell state generation in coupled quantum dots
We investigate the dynamics of two interacting electrons in coupled quantum
dots driven by an AC field. We find that the two electrons can be trapped in
one of the dots by the AC field, in spite of the strong Coulomb repulsion. In
particular, we find that the interaction may enhance the localization effect.
We also demonstrate the field excitation procedure to generate the maximally
entangled Bell states. The generation time is determined by both analytic and
numerical solutions of the time dependent Schrodinger equation.Comment: 12 pages, 5 figure
Vortex microavalanches in superconducting Pb thin films
Local magnetization measurements on 100 nm type-II superconducting Pb thin
films show that flux penetration changes qualitatively with temperature. Small
flux jumps at the lowest temperatures gradually increase in size, then
disappear near T = 0.7Tc. Comparison with other experiments suggests that the
avalanches correspond to dendritic flux protrusions. Reproducibility of the
first flux jumps in a decreasing magnetic field indicates a role for defect
structure in determining avalanches. We also find a temperature-independent
final magnetization after flux jumps, analogous to the angle of repose of a
sandpile.Comment: 6 pages, 5 figure
Entanglement in Weisskopf-Wigner theory of atomic decay in free space
In this paper, we use the Weisskopf-Wigner theory to study the entanglement
in the state of the free-space radiation field produced from vacuum due to
atomic decay. We show how bipartite entanglement is shared between different
partitions of the radiation modes. We investigate the role played by the size
of the partitions and their detuning with the decaying atom. The dynamics of
the atom-field entanglement during the atomic decay is also briefly discussed.
From this dynamics, we assert that such entanglement is the physical quantity
that fix the statistical atomic decay time.Comment: 7 pages, 4 figures, changed from purity to entropy of entanglement
calculations in the replaced versio
The indispensable role of the transversal spin fluctuations mechanism in laser-induced demagnetization of Co/Pt multilayers with nanoscale magnetic domains
The switching of magnetic domains induced by an ultrashort laser pulse has been demonstrated in nanostructured ferromagnetic films. This leads to the dawn of a new era in breaking the ultimate physical limit for the speed of magnetic switching and manipulation, which is relevant to current and future information storage. However, our understanding of the interactions between light and spins in magnetic heterostructures with nanoscale domain structures is still lacking. Here, both time-resolved magneto-optical Kerr effect experiments and atomistic simulations are carried out to investigate the dominant mechanism of laser-induced ultrafast demagnetization in [Co/Pt]20 multilayers with nanoscale magnetic domains. It is found that the ultrafast demagnetization time remains constant with various magnetic configurations, indicating that the domain structures play a minor role in laser-induced ultrafast demagnetization. In addition, both in experiment and atomistic simulations, we find a dependence of ultrafast demagnetization time τ M on the laser fluence, which is in contrast to the observations of spin transport within magnetic domains. The remarkable agreement between experiment and atomistic simulations indicates that the local dissipation of spin angular momentum is the dominant demagnetization mechanism in this system. More interestingly, we made a comparison between the atomistic spin dynamic simulation and the longitudinal spin flip model, highlighting that the transversal spin fluctuations mechanism is responsible for the ultrafast demagnetization in the case of inhomogeneous magnetic structures. This is a significant advance in clarifying the microscopic mechanism underlying the process of ultrafast demagnetization in inhomogeneous magnetic structures
Measurement of W Polarisation at LEP
The three different helicity states of W bosons produced in the reaction e+
e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W
decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to
measure the polarisation of W bosons, and its dependence on the W boson
production angle. The fraction of longitudinally polarised W bosons is measured
to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and
the second systematic, in agreement with the Standard Model expectation
Search for Anomalous Couplings in the Higgs Sector at LEP
Anomalous couplings of the Higgs boson are searched for through the processes
e^+ e^- -> H gamma, e^+ e^- -> e^+ e^- H and e^+ e^- -> HZ. The mass range 70
GeV < m_H < 190 GeV is explored using 602 pb^-1 of integrated luminosity
collected with the L3 detector at LEP at centre-of-mass energies
sqrt(s)=189-209 GeV. The Higgs decay channels H -> ffbar, H -> gamma gamma, H
-> Z\gamma and H -> WW^(*) are considered and no evidence is found for
anomalous Higgs production or decay. Limits on the anomalous couplings d, db,
Delta(g1z), Delta(kappa_gamma) and xi^2 are derived as well as limits on the H
-> gamma gamma and H -> Z gamma decay rates
Measurement of W Polarisation at LEP
The three different helicity states of W bosons produced in the reaction e+
e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W
decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to
measure the polarisation of W bosons, and its dependence on the W boson
production angle. The fraction of longitudinally polarised W bosons is measured
to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and
the second systematic, in agreement with the Standard Model expectation
Bose-Einstein Correlations of Neutral and Charged Pions in Hadronic Z Decays
Bose-Einstein correlations of both neutral and like-sign charged pion pairs
are measured in a sample of 2 million hadronic Z decays collected with the L3
detector at LEP. The analysis is performed in the four-momentum difference
range 300 MeV < Q < 2 GeV. The radius of the neutral pion source is found to be
smaller than that of charged pions. This result is in qualitative agreement
with the string fragmentation model
- …