81 research outputs found
Microscopic Theory of Scattering of Weak Electromagnetic Radiation by a Dense Ensemble of Ultracold Atoms
Based on the developed quantum microscopic theory, the interaction of weak
electromagnetic radiation with dense ultracold atomic clouds is described in
detail. The differential and total cooperative scattering cross sections are
calculated for monochromatic radiation as particular examples of application of
the general theory. The angular, spectral, and polarization properties of
scattered light are determined. The dependence of these quantities on the
sample size and concentration of atoms is studied and the influence of
collective effects is analyzed
Studying Millisecond Pulsars in X-rays
Millisecond pulsars represent an evolutionarily distinct group among rotation-powered pulsars. Outside the radio band, the soft X-ray range (--10 keV) is most suitable for studying radiative mechanisms operating in these fascinating objects. X-ray observations revealed diverse properties of emission from millisecond pulsars. For the most of them, the bulk of radiation is of a thermal origin, emitted from small spots (polar caps) on the neutron star surface heated by relativistic particles produced in pulsar acceleration zones. On the other hand, a few other very fast rotating pulsars exhibit almost pure nonthermal emission generated, most probably, in pulsar magnetospheres. There are also examples of nonthermal emission detected from X-ray nebulae powered by millisecond pulsars, as well as from pulsar winds shocked in binary systems with millisecond pulsars as companions. These and other most important results obtained from X-ray observations of millisecond pulsars are reviewed in this paper, as well as results from the search for millisecond pulsations in X-ray flux of the radio-quite neutron star RX J1856.5-3754
Cavity electromagnetically induced transparency and all-optical switching using ion Coulomb crystals
The control of one light field by another, ultimately at the single photon
level, is a challenging task which has numerous interesting applications within
nonlinear optics and quantum information science. Due to the extremely weak
direct interactions between optical photons in vacuum, this type of control can
in practice only be achieved through highly nonlinear interactions within a
medium. Electromagnetic induced transparency (EIT) constitutes one such means
to obtain the extremely strong nonlinear coupling needed to facilitate
interactions between two faint light fields. Here, we demonstrate for the first
time EIT as well as all-optical EIT-based light switching using ion Coulomb
crystals situated in an optical cavity. Unprecedented narrow cavity EIT feature
widths down to a few kHz and a change from essentially full transmission to
full absorption of the probe field within a window of only ~100 kHz are
achieved. By applying a weak switching field, we furthermore demonstrate nearly
perfect switching of the transmission of the probe field. These results
represent important milestones for future realizations of quantum information
processing devices, such as high-efficiency quantum memories, single-photon
transistors and single-photon gates
Symmetry of the Neutron and Proton Superfluidity Effects in Cooling Neutron Stars
We investigate the combined effect of neutron and proton superfluidities on
the cooling of neutron stars whose cores consist of nucleons and electrons. We
consider singlet-state pairing of protons and triplet-state pairing of neutrons
in the cores of neutron stars. The critical superfluid temperatures T_c are
assumed to depend on the density of matter. We study two types of neutron
pairing with different components of the total angular momentum of Cooper pairs
along the quantization axis (|m_J| =0 or 2). Our calculations are compared with
observations of thermal emission from isolated neutron stars. We show that the
observations can be interpreted by using two classes of superfluidity models:
(1) strong proton superfluidity with a maximum critical temperature in the
stellar core T_c^{max} > 4 \times 10^9 K and weak neutron superfluidity of any
type (T_c^{max} < 2 \times 10^8 K); (2) strong neutron superfluidity (pairing
with |m_J|=0) and weak proton superfluidity. The two types of models reflect an
approximate symmetry with respect to an interchange of the critical
temperatures of neutron and proton pairing.Comment: 20 pages, 8 figure
Atomic spectroscopy on a chip
Abstract: We demonstrate the ability to generate extremely large rubidium densities in uncoated hollow-core photonic band-gap fibers using lightinduced atomic desorption. Once the fiber is exposed to Rb vapor for 1-2 weeks, and this atomic source is removed, the fiber yields large desorbable densities for an extended period of time. We show that optical depths greater than e -1200 can be created within seconds. Our observed Rb densities are several orders of magnitude larger than any previously reported to be generated optically, and allow for the demonstration of a relatively easy-touse fiber-based vapor cell capable of producing large optical depths without the need for thermal tuning. H. Schmidt and A. Imamoğlu, "Giant Kerr nonlinearities obtained by electromagnetically-induced transparency," Opt. Lett. 21, 1936Lett. 21, -1938Lett. 21, (199
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Ecological Change on California’s Channel Islands from the Pleistocene to the Anthropocene
Historical ecology is becoming an important focus in conservation biology and offers a promising tool to help guide ecosystem management.
Here, we integrate data from multiple disciplines to illuminate the past, present, and future of biodiversity on California’s Channel Islands, an
archipelago that has undergone a wide range of land-use and ecological changes. Our analysis spans approximately 20,000 years, from before
human occupation and through Native American hunter–gatherers, commercial ranchers and fishers, the US military, and other land managers.
We demonstrate how long-term, interdisciplinary research provides insight into conservation decisions, such as setting ecosystem restoration
goals, preserving rare and endemic taxa, and reducing the impacts of climate change on natural and cultural resources. We illustrate the
importance of historical perspectives for understanding modern patterns and ecological change and present an approach that can be applied
generally in conservation management planning.Keywords: novel ecosystems, historical ecology, restoration, conservatio
Truncation of the Accretion Disk at One-third of the Eddington Limit in the Neutron Star Low-mass X-Ray Binary Aquila X-1
We perform a reflection study on a new observation of the neutron star
low-mass X-ray binary Aquila X-1 taken with NuSTAR during the August 2016
outburst and compare with the July 2014 outburst. The source was captured at
, which is over four times more luminous than the
previous observation during the 2014 outburst. Both observations exhibit a
broadened Fe line profile. Through reflection modeling, we determine that the
inner disk is truncated (where
) and (errors quoted at the 90%
confidence level). Fiducial neutron star parameters (M M,
km) give a stellar radius of ; our measurements
rule out a disk extending to that radius at more than the level of
confidence. We are able to place an upper limit on the magnetic field strength
of G at the magnetic poles, assuming that the disk
is truncated at the magnetospheric radius in each case. This is consistent with
previous estimates of the magnetic field strength for Aquila X-1. However, if
the magnetosphere is not responsible for truncating the disk prior to the
neutron star surface, we estimate a boundary layer with a maximum extent of
and . Additionally, we
compare the magnetic field strength inferred from the Fe line profile of Aquila
X-1 and other neutron star low-mass X-ray binaries to known accreting
millisecond X-ray pulsars.Comment: Accepted for publication in ApJ, 7 pages, 2 Tables, 5 Figure
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