146 research outputs found
Continuous Entanglement Distribution from an AlGaAs-on-Insulator Microcomb for Quantum Communications
Using an aluminum gallium arsenide microring resonator, we demonstrate a
bright quantum optical microcomb with nm bandwidth and more than 20 sets
of time-energy entangled modes, enabling spectral demultiplexing with simple,
off-the-shelf commercial telecom components. We report high-rate continuous
entanglement distribution for two sets of entangled-photon pair frequency modes
exhibiting up to GHz/mW pair generation rate. As an illustrative
example of entanglement distribution, we perform a continuous-wave time-bin
quantum key distribution protocol with 8 kbps raw key rates while maintaining
less than 10 error rate and sufficient two-photon visibility to ensure
security of the channel. When the 20 frequency modes are multiplexed, we
estimate 100 kbps entanglement-based key rates or the creation of a
multi-user quantum communications network. The entire system requires less than
110 W of on-chip optical power, demonstrating an efficient source of
entangled frequency modes for quantum communications. As a proof of principle,
a quantum key is distributed across 12 km of deployed fiber on the UCSB campus
and used to transmit a 21 kB image with error.Comment: 14 pages, 8 figure
The VIRUS-P Exploration of Nearby Galaxies (VENGA): Survey Design and First Results
VENGA is a large-scale extragalactic IFU survey, which maps the bulges, bars
and large parts of the outer disks of 32 nearby normal spiral galaxies. The
targets are chosen to span a wide range in Hubble types, star formation
activities, morphologies, and inclinations, at the same time of having vast
available multi-wavelength coverage from the far-UV to the mid-IR, and
available CO and 21cm mapping. The VENGA dataset will provide 2D maps of the
SFR, stellar and gas kinematics, chemical abundances, ISM density and
ionization states, dust extinction and stellar populations for these 32
galaxies. The uniqueness of the VIRUS-P large field of view permits these
large-scale mappings to be performed. VENGA will allow us to correlate all
these important quantities throughout the different environments present in
galactic disks, allowing the conduction of a large number of studies in star
formation, structure assembly, galactic feedback and ISM in galaxies.Comment: 7 pages, 3 figures, proceedings of the "Third Biennial Frank N. Bash
Symposium, New Horizons in Astronomy" held in Austin, TX, Oct. 2009. To be
published in the Astronomical Society of the Pacific Conference Series, eds.
L. Stanford, L. Hao, Y. Mao, J. Gree
Pressure-induced dimerization and collapse of antiferromagnetism in the Kitaev material α−Li2IrO3
We present magnetization measurements carried out on polycrystalline and
single-crystalline samples of -LiIrO under hydrostatic
pressures up to 2 GPa and establish the temperature-pressure phase diagram of
this material. The N\'eel temperature () of -LiIrO
is slightly enhanced upon compression with = 1.5 K/GPa. Above
1.2 GPa, -LiIrO undergoes a first-order phase transition toward
a nonmagnetic dimerized phase, with no traces of the magnetic phase observed
above 1.8 GPa at low temperatures. The critical pressure of the structural
dimerization is strongly temperature-dependent. This temperature dependence is
well reproduced on the ab initio level by taking into account lower phonon
entropy in the nonmagnetic phase. We further show that the initial increase in
of the magnetic phase is due to a weakening of the Kitaev
interaction along with the enhancement of the Heisenberg term and
off-diagonal anisotropy . Our study reveals a common thread in the
interplay of magnetism and dimerization in pressured Kitaev materials.Comment: 8 pages, 7 figure
Phase Transitions, Inhomogeneous Horizons and Second-Order Hydrodynamics
We use holography to study the spinodal instability of a four-dimensional, strongly-coupled gauge theory with a first-order thermal phase transition. We place the theory on a cylinder in a set of homogeneous, unstable initial states. The dual gravity configurations are black branes afflicted by a Gregory-Laflamme instability. We numerically evolve Einstein's equations to follow the instability until the system settles down to a stationary, inhomogeneous black brane. The dual gauge theory states have constant temperature but non-constant energy density. We show that the time evolution of the instability and the final states are accurately described by second-order hydrodynamics. In the static limit, the latter reduces to a single, second-order, non-linear differential equation from which the inhomogeneous final states can be derived
Bulges Of Nearby Galaxies With Spitzer: The Growth Of Pseudobulges In Disk Galaxies And Its Connection To Outer Disks
We study star formation rates (SFR) and stellar masses in bulges of nearby
disk galaxies, using SFRs and stellar masses derived from Spitzer and GALEX
data. At present day SFR the median pseudobulge could have grown the present
day stellar mass in 8 Gyr. In almost all galaxies in our sample the specific
SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer
disk, suggesting that almost all galaxies are increasing their B/T through
internal star formation. In pseudobulges, SFR density correlates, positvely,
with mass density, this is consistent with that stellar mass being formed by
moderate, extended star fromation. As well, SFR density and stellar mass of
pseudobulges are shown to be correlated with the stellar mass of the outer
disk. Classical bulges have the lowest specific SFR implying a growth times
that are longer than a Hubble time. We identify a class of bulges that have
nuclear morphology similar to pseudobulges, significantly lower specific SFR
than pseudobulges, and are closer to classical bulges in structural parameter
correlations. Our results are consistent with a scenario in which bulge growth
via internal star formation is a natural, and near ubiquitous phenomenon in
disk galaxies. Some disk galaxies with out a large classical bulge, over long
periods of extended star formation are able to growth a pseudobulge. In this
sense, galaxies with pseudobulges may very well be bulgeless (or
"quasi-bulgeless") galaxies, and galaxies with classical bulges are galaxies in
which both internal evolution and hierarchical merging are responsible for the
bulge mass by fractions that vary from galaxy-to-galaxy. [Abridged]Comment: Accepted to Ap
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