7,814 research outputs found
Spin squeezing of atomic ensembles by multi-colour quantum non-demolition measurements
We analyze the creation of spin squeezed atomic ensembles by simultaneous
dispersive interactions with several optical frequencies. A judicious choice of
optical parameters enables optimization of an interferometric detection scheme
that suppresses inhomogeneous light shifts and keeps the interferometer
operating in a balanced mode that minimizes technical noise. We show that when
the atoms interact with two-frequency light tuned to cycling transitions the
degree of spin squeezing scales as where is the
resonant optical depth of the ensemble. In real alkali atoms there are loss
channels and the scaling may be closer to Nevertheless
the use of two-frequencies provides a significant improvement in the degree of
squeezing attainable as we show by quantitative analysis of non-resonant
probing on the Cs D1 line. Two alternative configurations are analyzed: a
Mach-Zehnder interferometer that uses spatial interference, and an interaction
with multi-frequency amplitude modulated light that does not require a spatial
interferometer.Comment: 7 figure
Observation of quantum spin noise in a 1D light-atoms quantum interface
We observe collective quantum spin states of an ensemble of atoms in a
one-dimensional light-atom interface. Strings of hundreds of cesium atoms
trapped in the evanescent fiel of a tapered nanofiber are prepared in a
coherent spin state, a superposition of the two clock states. A weak quantum
nondemolition measurement of one projection of the collective spin is performed
using a detuned probe dispersively coupled to the collective atomic observable,
followed by a strong destructive measurement of the same spin projection. For
the coherent spin state we achieve the value of the quantum projection noise 40
dB above the detection noise, well above the 3 dB required for reconstruction
of the negative Wigner function of nonclassical states. We analyze the effects
of strong spatial inhomogeneity inherent to atoms trapped and probed by the
evanescent waves. We furthermore study temporal dynamics of quantum
fluctuations relevant for measurement-induced spin squeezing and assess the
impact of thermal atomic motion. This work paves the road towards observation
of spin squeezed and entangled states and many-body interactions in 1D spin
ensembles
Modeling edge effects of mesa diodes for silicon photovoltaics
A mesa diode has been modeled and its performance under dark and illuminated conditions has been simulated using a commercial finite element software package. These simulations have led to a determination of the self-consistent solution to the continuity equations for electrons and holes using the steady-state drift-diffusion model for carrier dynamics coupled with electric potential determined from Poisson\u27s equation. The purpose of these simulations has been to determine the influence of edge conditions on the overall performance of mesa diodes under dark and illuminated conditions.
Mesa diode arrays are fabricated on crystalline silicon solar cells. They are an array of small area solar cells that are electrically isolated from one another. They can be probed to spatially measure the current density vs. voltage curves under dark and illuminated conditions. The underlying models of bulk and surface recombination mechanisms have been well established for crystalline silicon based semiconductor devices such as the mesa diode. However, the combination of these phenomena that occur during the simulation of the operation of the mesa diode results in a unique edge effect that can significantly change the overall performance of the mesa diode. In particular, the simulations performed show that the space charge region becomes extended along the vertical edge of the mesa diode due to the fixed positive surface charge. At the intersection of the vertical edge and step, a strong electric field is produced because it has a small convex radius of curvature. Depending on the sharpness of this intersection, the entire device can become significantly shunted. Simulations have been performed with a sharp corner and a smooth curve at the intersection of the vertical edge and the step. The use of a smooth curved transition results in significantly lower dark current density vs. voltage and a greater open circuit voltage and fill factor under illumination. Yet, even with a curved transition, the space charge region can extend approximately 100 microns into a 199.5 micron thick mesa diode, and have a bulk recombination rate that is two orders of magnitude greater than the rest of the device at low forward biases
Generation and detection of a sub-Poissonian atom number distribution in a one-dimensional optical lattice
We demonstrate preparation and detection of an atom number distribution in a
one-dimensional atomic lattice with the variance dB below the Poissonian
noise level. A mesoscopic ensemble containing a few thousand atoms is trapped
in the evanescent field of a nanofiber. The atom number is measured through
dual-color homodyne interferometry with a pW-power shot noise limited probe.
Strong coupling of the evanescent probe guided by the nanofiber allows for a
real-time measurement with a precision of atoms on an ensemble of some
atoms in a one-dimensional trap. The method is very well suited for
generating collective atomic entangled or spin-squeezed states via a quantum
non-demolition measurement as well as for tomography of exotic atomic states in
a one-dimensional lattice
Ascorbic acid enhances the inhibitory effect of aspirin on neuronal cyclooxygenase-2-mediated prostaglandin E2 production.
Inhibition of neuronal cyclooxygenase-2 (COX-2) and hence prostaglandin E2 (PGE2) synthesis by non-steroidal anti-inflammatory drugs has been suggested to protect neuronal cells in a variety of pathophysiological situations including Alzheimer's disease and ischemic stroke. Ascorbic acid (vitamin C) has also been shown to protect cerebral tissue in a variety of experimental conditions, which has been attributed to its antioxidant capacity. In the present study, we show that ascorbic acid dose-dependently inhibited interleukin-1beta (IL-1beta)-mediated PGE2 synthesis in the human neuronal cell line, SK-N-SH. Furthermore, in combination with aspirin, ascorbic acid augmented the inhibitory effect of aspirin on PGE2 synthesis. However, ascorbic acid had no synergistic effect along with other COX inhibitors (SC-58125 and indomethacin). The inhibition of IL-1beta-mediated PGE2 synthesis by ascorbic acid was not due to the inhibition of the expression of COX-2 or microsomal prostaglandin E synthase (mPGES-1). Rather, ascorbic acid dose-dependently (0.1-100 microM) produced a significant reduction in IL-1beta-mediated production of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a reliable indicator of free radical formation, suggesting that the effects of ascorbic acid on COX-2-mediated PGE2 biosynthesis may be the result of the maintenance of the neuronal redox status since COX activity is known to be enhanced by oxidative stress. Our results provide in vitro evidence that the neuroprotective effects of ascorbic acid may depend, at least in part, on its ability to reduce neuronal COX-2 activity and PGE2 synthesis, owing to its antioxidant properties. Further, these experiments suggest that a combination of aspirin with ascorbic acid constitutes a novel approach to render COX-2 more sensitive to inhibition by aspirin, allowing an anti-inflammatory therapy with lower doses of aspirin, thereby avoiding the side effects of the usually high dose aspirin treatment
Developments in Rare Kaon Decay Physics
We review the current status of the field of rare kaon decays. The study of
rare kaon decays has played a key role in the development of the standard
model, and the field continues to have significant impact. The two areas of
greatest import are the search for physics beyond the standard model and the
determination of fundamental standard-model parameters. Due to the exquisite
sensitivity of rare kaon decay experiments, searches for new physics can probe
very high mass scales. Studies of the k->pnn modes in particular, where the
first event has recently been seen, will permit tests of the standard-model
picture of quark mixing and CP violation.Comment: One major revision to the text is the branching ratio of KL->ppg,
based on a new result from KTeV. Several references were updated, with minor
modifications to the text. A total of 48 pages, with 28 figures, in LaTeX; to
be published in the Annual Review of Nuclear and Particle Science, Vol. 50,
December 200
Photoemission spectroscopy and sum rules in dilute electron-phonon systems
A family of exact sum rules for the one-polaron spectral function in the
low-density limit is derived. An algorithm to calculate energy moments of
arbitrary order of the spectral function is presented. Explicit expressions are
given for the first two moments of a model with general electron-phonon
interaction, and for the first four moments of the Holstein polaron. The sum
rules are linked to experiments on momentum-resolved photoemission
spectroscopy. The bare electronic dispersion and the electron-phonon coupling
constant can be extracted from the first and second moments of spectrum. The
sum rules could serve as constraints in analytical and numerical studies of
electron-phonon models.Comment: 4 page
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