143,177 research outputs found
Efficient Scheme for Perfect Collective Einstein-Podolsky-Rosen Steering
A practical scheme for the demonstration of perfect one-sided
device-independent quantum secret sharing is proposed. The scheme involves a
three-mode optomechanical system in which a pair of independent cavity modes is
driven by short laser pulses and interact with a movable mirror. We demonstrate
that by tuning the laser frequency to the blue (anti-Stokes) sideband of the
average frequency of the cavity modes, the modes become mutually coherent and
then may collectively steer the mirror mode to a perfect
Einstein-Podolsky-Rosen state. The scheme is shown to be experimentally
feasible, it is robust against the frequency difference between the modes,
mechanical thermal noise and damping, and coupling strengths of the cavity
modes to the mirror.Comment: 9 pages, 4 figure
Spin-polarized quantum transport through a T-shape quantum dot-array: a model of spin splitter
We in this paper study theoretically the spin-polarized quantum transport
through a T-shape quantum dot-array by means of transfer-matrix method along
with the Green^{,}s function technique. Multi-magnetic fields are used to
produce the spin-polarized transmission probabilities and therefore the spin
currents, which are shown to be tunable in a wide range by adjusting the
energy, and the direction-angle of magnetic fields as well. Particularly the
opposite- spin- polarization currents separately flowing out to two electrodes
can be generated and thus the system acts as a spin splitter.Comment: 8 pages, 8 figure
Periodicities in Solar Coronal Mass Ejections
Mid-term quasi-periodicities in solar coronal mass ejections (CMEs) during
the most recent solar maximum cycle 23 are reported here for the first time
using the four-year data (February 5, 1999 to February 10, 2003) of the Large
Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO). In parallel, mid-term quasi-periodicities in solar X-ray
flares (class >M5.0) from the Geosynchronous Operational Environment Satellites
(GOES) and in daily averages of Ap index for geomagnetic disturbances from the
World Data Center (WDC) at the International Association for Geomagnetism and
Aeronomy (IAGA) are also examined for the same four-year time span. Several
conceptual aspects of possible equatorially trapped Rossby-type waves at and
beneath the solar photosphere are discussed.Comment: Accepted by MNRAS, 6 figure
Ground state of spin-1 Bose-Einstein condensates with spin-orbit coupling in a Zeeman field
We systematically investigate the weakly trapped spin-1 Bose-Einstein
condensates with spin-orbit coupling in an external Zeeman field. We find that
the mean-field ground state favors either a magnetized standing wave phase or
plane wave phase when the strength of Zeeman field is below a critical value
related to the strength of spin-orbit coupling. Zeeman field can induce the
phase transition between standing wave and plane wave phases, and we determine
the phase boundary analytically and numerically. The magnetization of these two
phases responds to the external magnetic field in a very unique manner, the
linear Zeeman effect magnetizes the standing wave phase along the direction of
the magnetic field, but the quadratic one demagnetizes the plane wave phase.
When the strength of Zeeman field surpasses the critical value, the system is
completely polarized to a ferromagnetic state or polar state with zero
momentum
A Novel Large Moment Antiferromagnetic Order in K0.8Fe1.6Se2 Superconductor
The discovery of cuprate high Tc superconductors has inspired searching for
unconventional su- perconductors in magnetic materials. A successful recipe has
been to suppress long-range order in a magnetic parent compound by doping or
high pressure to drive the material towards a quantum critical point, which is
replicated in recent discovery of iron-based high TC superconductors. The
long-range magnetic order coexisting with superconductivity has either a small
magnetic moment or low ordering temperature in all previously established
examples. Here we report an exception to this rule in the recently discovered
potassium iron selenide. The superconducting composition is identified as the
iron vacancy ordered K0.8Fe1.6Se2 with Tc above 30 K. A novel large moment 3.31
{\mu}B/Fe antiferromagnetic order which conforms to the tetragonal crystal
symmetry has the unprecedentedly high an ordering temperature TN = 559 K for a
bulk superconductor. Staggeredly polarized electronic density of states thus is
suspected, which would stimulate further investigation into superconductivity
in a strong spin-exchange field under new circumstance.Comment: 5 figures, 5 pages, and 2 tables in pdf which arXiv.com cannot tak
Abell 2111: An Optical and Radio Study of the Richest Butcher-Oemler Cluster
We present an in-depth analysis of the Butcher-Oemler cluster A2111,
including new optical spectroscopy plus a deep Very Large Array (VLA) radio
continuum observation. These are combined with optical imaging from the Sloan
Digital Sky Survey (SDSS) to assess the activity and properties of member
galaxies. Prior X-ray studies have suggested A2111 is a head-on cluster merger,
a dynamical state which might be connected to the high level of activity
inferred from its blue fraction. We are able to directly assess this claim,
using our spectroscopic data to identify 95 cluster members among 196 total
galaxy spectra. These galaxy velocities do not themselves provide significant
evidence for the merger interpretation, however they are consistent with it
provided the system is viewed near the time of core passage and at a viewing
angle >~30 degrees different from the merger axis. The SDSS data allow us to
confirm the high blue fraction for A2111, f_b = 0.15 +/- 0.03 based on
photometry alone and f_b = 0.23 +/- 0.03 using spectroscopic data to remove
background galaxies. We are able to detect 175 optical sources from the SDSS in
our VLA radio data, of which 35 have redshift information. We use the SDSS
photometry to determine photometric redshifts for the remaining 140
radio-optical sources. In total we identify up to 26 cluster radio galaxies, 14
of which have spectroscopic redshifts. The optical spectroscopy and radio data
reveal a substantial population of dusty starbursts within the cluster. The
high blue fraction and prevalence of star formation is consistent with the
hypothesis that dynamically-active clusters are associated with more active
member galaxies than relaxed clusters.Comment: To appear in AJ; 53 pages including 10 figures and several long
table
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