414 research outputs found
Cavity Magnonics
Cavity magnonics deals with the interaction of magnons - elementary excitations in magnetic materials - and confined electromagnetic fields. We introduce the basic physics and review the experimental and theoretical progress of this young field that is gearing up for integration in future quantum technologies. Much of its appeal is derived from the strong magnon-photon coupling and the easily-reached nonlinear regime in microwave cavities. The interaction of magnons with light as detected by Brillouin light scattering is enhanced in magnetic optical resonators, which can be employed to manipulate magnon distributions. The cavity photon-mediated coupling of a magnon mode to a superconducting qubit enables measurements in the single magnon limit
Verification of the Kepler Input Catalog from Asteroseismology of Solar-type Stars
We calculate precise stellar radii and surface gravities from the
asteroseismic analysis of over 500 solar-type pulsating stars observed by the
Kepler space telescope. These physical stellar properties are compared with
those given in the Kepler Input Catalog (KIC), determined from ground-based
multi-color photometry. For the stars in our sample, we find general agreement
but we detect an average overestimation bias of 0.23 dex in the KIC
determination of log (g) for stars with log (g)_KIC > 4.0 dex, and a resultant
underestimation bias of up to 50% in the KIC radii estimates for stars with
R_KIC < 2 R sun. Part of the difference may arise from selection bias in the
asteroseismic sample; nevertheless, this result implies there may be fewer
stars characterized in the KIC with R ~ 1 R sun than is suggested by the
physical properties in the KIC. Furthermore, if the radius estimates are taken
from the KIC for these affected stars and then used to calculate the size of
transiting planets, a similar underestimation bias may be applied to the
planetary radii.Comment: Published in The Astrophysical Journal Letter
Predicting the detectability of oscillations in solar-type stars observed by Kepler
Asteroseismology of solar-type stars has an important part to play in the
exoplanet program of the NASA Kepler Mission. Precise and accurate inferences
on the stellar properties that are made possible by the seismic data allow very
tight constraints to be placed on the exoplanetary systems. Here, we outline
how to make an estimate of the detectability of solar-like oscillations in any
given Kepler target, using rough estimates of the temperature and radius, and
the Kepler apparent magnitude.Comment: 21 pages, 6 figures, accepted for publication Astrophysical Journa
A uniform asteroseismic analysis of 22 solar-type stars observed by Kepler
Asteroseismology with the Kepler space telescope is providing not only an
improved characterization of exoplanets and their host stars, but also a new
window on stellar structure and evolution for the large sample of solar-type
stars in the field. We perform a uniform analysis of 22 of the brightest
asteroseismic targets with the highest signal-to-noise ratio observed for 1
month each during the first year of the mission, and we quantify the precision
and relative accuracy of asteroseismic determinations of the stellar radius,
mass, and age that are possible using various methods. We present the
properties of each star in the sample derived from an automated analysis of the
individual oscillation frequencies and other observational constraints using
the Asteroseismic Modeling Portal (AMP), and we compare them to the results of
model-grid-based methods that fit the global oscillation properties. We find
that fitting the individual frequencies typically yields asteroseismic radii
and masses to \sim1% precision, and ages to \sim2.5% precision (respectively 2,
5, and 8 times better than fitting the global oscillation properties). The
absolute level of agreement between the results from different approaches is
also encouraging, with model-grid-based methods yielding slightly smaller
estimates of the radius and mass and slightly older values for the stellar age
relative to AMP, which computes a large number of dedicated models for each
star. The sample of targets for which this type of analysis is possible will
grow as longer data sets are obtained during the remainder of the mission.Comment: 13 pages, 5 figures in the main text, 22 figures in Appendix.
Accepted for publication in Ap
Energy dependent counting statistics in diffusive superconducting tunnel junctions
We present an investigation of the energy dependence of the full charge
counting statistics in diffusive
normal-insulating-normal-insulating-superconducting junctions. It is found that
the current in general is transported via a correlated transfer of pairs of
electrons. Only in the case of strongly asymmetric tunnel barriers or energies
much larger than the Thouless energy is the pair transfer uncorrelated. The
second cumulant, the noise, is found to depend strongly on the applied voltage
and temperature. For a junction resistance dominated by the tunnel barrier to
the normal reservoir, the differential shot noise shows a double peak feature
at voltages of the order of the Thouless energy, a signature of an ensemble
averaged electron-hole resonance.Comment: 8 pages, 5 figure
A precise asteroseismic age and radius for the evolved Sun-like star KIC 11026764
The primary science goal of the Kepler Mission is to provide a census of
exoplanets in the solar neighborhood, including the identification and
characterization of habitable Earth-like planets. The asteroseismic
capabilities of the mission are being used to determine precise radii and ages
for the target stars from their solar-like oscillations. Chaplin et al. (2010)
published observations of three bright G-type stars, which were monitored
during the first 33.5 days of science operations. One of these stars, the
subgiant KIC 11026764, exhibits a characteristic pattern of oscillation
frequencies suggesting that it has evolved significantly. We have derived
asteroseismic estimates of the properties of KIC 11026764 from Kepler
photometry combined with ground-based spectroscopic data. We present the
results of detailed modeling for this star, employing a variety of independent
codes and analyses that attempt to match the asteroseismic and spectroscopic
constraints simultaneously. We determine both the radius and the age of KIC
11026764 with a precision near 1%, and an accuracy near 2% for the radius and
15% for the age. Continued observations of this star promise to reveal
additional oscillation frequencies that will further improve the determination
of its fundamental properties.Comment: 16 pages, 6 figures, 4 tables, ApJ in pres
Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces
We investigate the transport properties of a ferromagnet-superconductor
interface within the framework of a modified three-dimensional
Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge
inhomogeneity forms via two unique transport mechanisms, namely, evanescent
Andreev reflection and evanescent quasiparticle transmission. Furthermore, we
take into account the influence of charge inhomogeneity on the interfacial
barrier potential and calculate the conductance as a function of bias voltage.
Point-contact Andreev reflection (PCAR) spectra often show dip structures,
large zero-bias conductance enhancement, and additional zero-bias conductance
peak. Our results indicate that transport-induced charge inhomogeneity could be
a source of all these anomalous characteristics of the PCAR spectra.Comment: 9 pages, 6 figure
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