12,944 research outputs found
Seeing bulk topological properties of band insulators in small photonic lattices
We present a general scheme for measuring the bulk properties of
non-interacting tight-binding models realized in arrays of coupled photonic
cavities. Specifically, we propose to implement a single unit cell of the
targeted model with tunable twisted boundary conditions in order to simulate
large systems and, most importantly, to access bulk topological properties
experimentally. We illustrate our method by demonstrating how to measure
topological invariants in a two-dimensional quantum Hall-like model.Comment: 5 pages, 2 figures; with Supplemental Material (2 pages
CP, T and CPT violation in future long baseline experiments
I give a short overview about the possibilities and problems related to the
measurement of CP violation in long baseline experiments. Special attention is
paid to the issue of degeneracies and a method for their resolution is
quantitatively discussed. The CP violation reach for different experiments is
compared in dependence of and \dm{21}. Furthermore a
short comment about the possible effects of matter induced T violation is made.
Finally the limits on CPT violation obtainable at a neutrino factory are shown.Comment: Talk presented at NUFACT02, London, 1-6 July, 2002. 3 pages, 2
figure
Probing of valley polarization in graphene via optical second-harmonic generation
Valley polarization in graphene breaks inversion symmetry and therefore leads
to second-harmonic generation. We present a complete theory of this effect
within a single-particle approximation. It is shown that this may be a
sensitive tool to measure the valley polarization created, e.g., by polarized
light and, thus, can be used for a development of ultrafast valleytronics in
graphene.Comment: 5 pages, 3 figure
Impact of the 3D source geometry on time-delay measurements of lensed type-Ia Supernovae
It has recently been proposed that gravitationally lensed type-Ia supernovae
can provide microlensing-free time-delay measurements provided that the
measurement is taken during the achromatic expansion phase of the explosion and
that color light curves are used rather than single-band light curves. If
verified, this would provide both precise and accurate time-delay measurements,
making lensed type-Ia supernovae a new golden standard for time-delay
cosmography. However, the 3D geometry of the expanding shell can introduce an
additional bias that has not yet been fully explored. In this work, we present
and discuss the impact of this effect on time-delay cosmography with lensed
supernovae and find that on average it leads to a bias of a few tenths of a day
for individual lensed systems. This is negligible in view of the cosmological
time delays predicted for typical lensed type-Ia supernovae but not for the
specific case of the recently discovered type-Ia supernova iPTF16geu, whose
time delays are expected to be smaller than a day.Comment: 7 pages, 4 figures, published in A&
Extension of the Schiff theorem to ions and molecules
According to the Schiff theorem the nuclear electric dipole moment (EDM) is
screened in neutral atoms. In ions this screening is incomplete. We extend a
derivation of the Schiff theorem to ions and molecules. The finite nuclear size
effects are considered including Z^2 alpha^2 corrections to the nuclear Schiff
moment which are significant in all atoms and molecules of experimental
interest. We show that in majority of ionized atoms the nuclear EDM
contribution to the atomic EDM dominates while in molecules the contribution of
the Schiff moment dominates. We also consider the screening of electron EDM in
ions
Improved modelling of liquid GeSe: the impact of the exchange-correlation functional
The structural properties of liquid GeSe are studied by using
first-principles molecular dynamics in conjuncton with the Becke, Lee, Yang and
Parr (BLYP) generalized gradient approximation for the exchange and correlation
energy. The results on partial pair correlation functions, coordination
numbers, bond angle distributions and partial structure factors are compared
with available experimental data and with previous first-principle molecular
dynamics results obtained within the Perdew and Wang (PW) generalized gradient
approximation for the exchange and correlation energy. We found that the BLYP
approach substantially improves upon the PW one in the case of the short-range
properties. In particular, the GeGe pair correlation function takes a more
structured profile that includes a marked first peak due to homopolar bonds, a
first maximum exhibiting a clear shoulder and a deep minimum, all these
features being absent in the previous PW results. Overall, the amount of
tetrahedral order is significantly increased, in spite of a larger number of
GeGe homopolar connections. Due to the smaller number of miscoordinations,
diffusion coefficients obtained by the present BLYP calculation are smaller by
at least one order of magnitude than in the PW case.Comment: 6 figure
Real-time observation of interfering crystal electrons in high-harmonic generation
Accelerating and colliding particles has been a key strategy to explore the
texture of matter. Strong lightwaves can control and recollide electronic
wavepackets, generating high-harmonic (HH) radiation which encodes the
structure and dynamics of atoms and molecules and lays the foundations of
attosecond science. The recent discovery of HH generation in bulk solids
combines the idea of ultrafast acceleration with complex condensed matter
systems and sparks hope for compact solid-state attosecond sources and
electronics at optical frequencies. Yet the underlying quantum motion has not
been observable in real time. Here, we study HH generation in a bulk solid
directly in the time-domain, revealing a new quality of strong-field
excitations in the crystal. Unlike established atomic sources, our solid emits
HH radiation as a sequence of subcycle bursts which coincide temporally with
the field crests of one polarity of the driving terahertz waveform. We show
that these features hallmark a novel non-perturbative quantum interference
involving electrons from multiple valence bands. The results identify key
mechanisms for future solid-state attosecond sources and next-generation
lightwave electronics. The new quantum interference justifies the hope for
all-optical bandstructure reconstruction and lays the foundation for possible
quantum logic operations at optical clock rates
On the improvement of the low energy neutrino factory
The low energy neutrino factory has been proposed as a very sensitive setup
for future searches for CP violation and matter effects. Here we study how its
performance is affected when the experimental specifications of the setup are
varied. Most notably, we have considered the addition of the 'platinum' nu_{mu}
-> nu_{e} channel. We find that, whilst theoretically the extra channel
provides very useful complementary information and helps to lift degeneracies,
its practical usefulness is lost when considering realistic background levels.
Conversely, an increase in statistics in the 'golden' nu_{e} -> nu_{mu} channel
and, to some extent, an improvement in the energy resolution, lead to an
important increase in the performance of the facility, given the rich energy
dependence of the 'golden' channel at these energies. We show that a low energy
neutrino factory with a baseline of 1300 km, muon energy of 4.5 GeV, and either
a 20 kton totally active scintillating detector or 100 kton liquid argon
detector, can have outstanding sensitivity to the neutrino oscillation
parameters theta13, delta and the mass hierarchy. For our estimated exposure of
2.8 x 10^{23} kton x decays per muon polarity, the low energy neutrino factory
has sensitivity to theta13 and delta for sin^{2}(2theta13) > 10^{-4} and to the
mass hierarchy for sin^{2}(2theta13) > 10^{-3}.Comment: 13 pages, 8 eps figures. Version published in PRD - experimental
section with preliminary results removed, abstract and conclusions re-written
accordingly, title changed, author list amended
Radiation intensities and heat-transfer in boiler furnaces
https://ir.uiowa.edu/uisie/1008/thumbnail.jp
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