493 research outputs found
A comparative study of overlap and staggered fermions in QCD
We perform a comparative study of the infrared properties of overlap and
staggered fermions in QCD. We observe that the infrared spectrum of the APE/HYP
improved staggered Dirac operator develops a four-fold near-degeneracy and is
in quantitative agreement with the infrared spectrum of the overlap operator.
The near-degeneracy allows us to identify the zero modes of the staggered
operator and we find that the number of zero modes is in line with the
topological index of the overlap operator.Comment: Talk presented at Lattice2004(chiral), Fermilab, June 21-26, 2004, 3
pages, 2 figure
Diffusion pathways of hydrogen across the steps of a vicinal Si(001) surface
Hydrogen diffusion across DB steps on Si(001) surfaces is investigated by means of variable-temperature scanning tunneling microscopy and first-principles calculations. Experimentally, the hopping rate for diffusion from the step sites to the Si dimers of the upper terrace was found to be more than one order of magnitude higher than that for diffusion to the lower terrace. This clear preference, opposite to the trend for the respective binding energies, is explained by first-principles calculations that identify a metastable intermediate to be responsible for the unexpected lowering of the energy barrier for upward diffusion
Dissociation of Feshbach Molecules into Different Partial Waves
Ultracold molecules can be associated from ultracold atoms by ramping the
magnetic field through a Feshbach resonance. A reverse ramp dissociates the
molecules. Under suitable conditions, more than one outgoing partial wave can
be populated. A theoretical model for this process is discussed here in detail.
The model reveals the connection between the dissociation and the theory of
multichannel scattering resonances. In particular, the decay rate, the
branching ratio, and the relative phase between the partial waves can be
predicted from theory or extracted from experiment. The results are applicable
to our recent experiment in 87Rb, which has a d-wave shape resonance.Comment: Added Refs.[32-38
Phase-dependent which-way information
We introduce a new observable for reading out a which-way detector in a
Young-type interferometer whose eigenstates either contain full which-way
information or none at all. We calculate the which-way knowledge K that can be
retrieved from this observable and find that K depends on the phase difference
\delta that the interfering object accumulates on its way from either slit to
the detector. In particular, it turns out that K(\delta) has an upper bound of
1, almost independent of the visibility V of the interference pattern generated
by the interfering object on a screen, which is in marked contrast to the
well-known inequality K^2 + V^2 <= 1 (cf. B.-G. Englert, Phys. Rev. Lett. 77,
2154 (1996)).Comment: 7 pages, 4 figure
Distributed Modeling and Parameter Estimation of Influenza Virus Replication During Vaccine Production
Lattice QCD at the physical point: Simulation and analysis details
We give details of our precise determination of the light quark masses
m_{ud}=(m_u+m_d)/2 and m_s in 2+1 flavor QCD, with simulated pion masses down
to 120 MeV, at five lattice spacings, and in large volumes. The details concern
the action and algorithm employed, the HMC force with HEX smeared clover
fermions, the choice of the scale setting procedure and of the input masses.
After an overview of the simulation parameters, extensive checks of algorithmic
stability, autocorrelation and (practical) ergodicity are reported. To
corroborate the good scaling properties of our action, explicit tests of the
scaling of hadron masses in N_f=3 QCD are carried out. Details of how we
control finite volume effects through dedicated finite volume scaling runs are
reported. To check consistency with SU(2) Chiral Perturbation Theory the
behavior of M_\pi^2/m_{ud} and F_\pi as a function of m_{ud} is investigated.
Details of how we use the RI/MOM procedure with a separate continuum limit of
the running of the scalar density R_S(\mu,\mu') are given. This procedure is
shown to reproduce the known value of r_0m_s in quenched QCD. Input from
dispersion theory is used to split our value of m_{ud} into separate values of
m_u and m_d. Finally, our procedure to quantify both systematic and statistical
uncertainties is discussed.Comment: 45 page
A Delayed Choice Quantum Eraser
This paper reports a "delayed choice quantum eraser" experiment proposed by
Scully and Dr\"{u}hl in 1982. The experimental results demonstrated the
possibility of simultaneously observing both particle-like and wave-like
behavior of a quantum via quantum entanglement. The which-path or both-path
information of a quantum can be erased or marked by its entangled twin even
after the registration of the quantum.Comment: twocolumn, 4pages, submitted to PR
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