1,215 research outputs found
Accessing higher order correlations by time-multiplexing
We experimentally measured higher order normalized correlation functions
(nCF) of pulsed light with a time-multiplexing-detector. We demonstrate
excellent performance of our device by verifying unity valued nCF up to the
eighth order for coherent light, and factorial dependence of the nCF for
pseudothermal light. We applied our measurement technique to a type-II
parametric downconversion source to investigate mutual two-mode correlation
properties and ascertain nonclassicality.Comment: 5 pages, 3 figure
K to pi and K to 0 in 2+1 Flavor Partially Quenched Chiral Perturbation Theory
We calculate results for K to pi and K to 0 matrix elements to
next-to-leading order in 2+1 flavor partially quenched chiral perturbation
theory. Results are presented for both the Delta I=1/2 and 3/2 channels, for
chiral operators corresponding to current-current, gluonic penguin, and
electroweak penguin 4-quark operators. These formulas are useful for studying
the chiral behavior of currently available 2+1 flavor lattice QCD results, from
which the low energy constants of the chiral effective theory can be
determined. The low energy constants of these matrix elements are necessary for
an understanding of the Delta I=1/2 rule, and for calculations of
epsilon'/epsilon using current lattice QCD simulations.Comment: 43 pages, 2 figures, uses RevTeX, added and updated reference
Counteranion-controlled properties of polyelectrolyte multilayers
Polyelectrolyte multilayers consisting of poly(diallyldimethylammonium chloride) (PDADMA) and poly(sodium 4-styrenesulfonate) (PSS) were studied on a quartz crystal microbalance (QCM) utilizing a novel method to determine the elastic properties of the films. Since the multilayer was found to consist of a hard core and soft outer layer, as can be realized on the basis of the multilayer zone model, the multilayer films were made thick enough to reveal the elastic properties of the bulk material of the film. Several hundreds of layers were deposited using a fully automated multilayer deposition machine. We found out that, in addition to the increase in the bilayer mass, a remarkable increase of stiffness of the polyelectrolyte multilayer was observed while changing the counteranion used in the deposition process. The increase of stiffness was found to be comparable to the glass transition of common polymers. The increase is attributed to the counteranions that take part in polyelectrolyte charge compensation. The correlation of storage shear modulus and mass density to the hydration entropy of the anion could be clearly observed
Modally Resolved Fabry-Perot Experiment with Semiconductor Waveguides
Based on the interaction between different spatial modes, semiconductor
Bragg-reflection waveguides provide a highly functional platform for non-linear
optics. Therefore, the control and engineering of the properties of each
spatial mode is essential. Despite the multimodeness of our waveguide, the
well-established Fabry-Perot technique for recording fringes in the optical
transmission spectrum can successfully be employed for a detailed linear
optical characterization when combined with Fourier analysis. A prerequisite
for the modal sensitivity is a finely resolved transmission spectrum that is
recorded over a broad frequency band. Our results highlight how the features of
different spatial modes, such as their loss characteristics and dispersion
properties, can be separated from each other allowing their comparison. The
mode-resolved measurements are important for optimizing the performance of such
multimode waveguides by tailoring the properties of their spatial modes.Comment: 8 pages, 7 figure
Direct probing of the Wigner function by time-multiplexed detection of photon statistics
We investigate the capabilities of loss-tolerant quantum state
characterization using a photon-number resolving, time-multiplexed detector
(TMD). We employ the idea of probing the Wigner function point-by-point in
phase space via photon parity measurements and displacement operations,
replacing the conventional homodyne tomography. Our emphasis lies on
reconstructing the Wigner function of non-Gaussian Fock states with highly
negative values in a scheme that is based on a realistic experimental setup. In
order to establish the concept of loss-tolerance for state characterization we
show how losses can be decoupled from the impact of other experimental
imperfections, i.e. the non-unity transmittance of the displacement
beamsplitter and non-ideal mode overlap. We relate the experimentally
accessible parameters to effective ones that are needed for an optimised state
reconstruction. The feasibility of our approach is tested by Monte Carlo
simulations, which provide bounds resulting from statistical errors that are
due to limited data sets. Our results clearly show that high losses can be
accepted for a defined parameter range, and moreover, that (in contrast to
homodyne detection) mode mismatch results in a distinct signature, which can be
evaluated by analysing the photon number oscillations of the displaced Fock
states.Comment: 22 pages, 13 figures, published versio
Staggered Chiral Perturbation Theory and the Fourth-Root Trick
Staggered chiral perturbation theory (schpt) takes into account the
"fourth-root trick" for reducing unwanted (taste) degrees of freedom with
staggered quarks by multiplying the contribution of each sea quark loop by a
factor of 1/4. In the special case of four staggered fields (four flavors,
nF=4), I show here that certain assumptions about analyticity and phase
structure imply the validity of this procedure for representing the rooting
trick in the chiral sector. I start from the observation that, when the four
flavors are degenerate, the fourth root simply reduces nF=4 to nF=1. One can
then treat nondegenerate quark masses by expanding around the degenerate limit.
With additional assumptions on decoupling, the result can be extended to the
more interesting cases of nF=3, 2, or 1. A apparent paradox associated with the
one-flavor case is resolved. Coupled with some expected features of unrooted
staggered quarks in the continuum limit, in particular the restoration of taste
symmetry, schpt then implies that the fourth-root trick induces no problems
(for example, a violation of unitarity that persists in the continuum limit) in
the lowest energy sector of staggered lattice QCD. It also says that the theory
with staggered valence quarks and rooted staggered sea quarks behaves like a
simple, partially-quenched theory, not like a "mixed" theory in which sea and
valence quarks have different lattice actions. In most cases, the assumptions
made in this paper are not only sufficient but also necessary for the validity
of schpt, so that a variety of possible new routes for testing this validity
are opened.Comment: 39 pages, 3 figures. v3: minor changes: improved explanations and
less tentative discussion in several places; corresponds to published versio
Core level spectroscopy of MoS2
X-ray photoelectron spectroscopy has been used to study mineral molybdenite, MoS2. The fitted core level spectra of sulphur 2p and molybdenum 3d states reveal several photon energy sensitive components. The high binding energy component in both spectra is proposed to originate from the uppermost sulphur or molybdenum atoms of an S-Mo-S sandwich layer of the hexagonal structure, respectively. The other features are suggested to be caused by the edge structures formed during the sample cleavage. The edge facets have much stronger chemical properties than the basal planes and they are known as the active sites of MoS2 when it is used as a catalyst. The spectral features and the effect of the structure of UHV cleaved MoS2 on them are discussed. (c) 2006 Elsevier B.V. All rights reserved
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