11,905 research outputs found
Entanglement, BEC, and superfluid-like behavior of two-mode photon systems
A system of two interacting photon modes, without constraints on the photon
number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer
amplitude is greater than the mode frequency. A symmetry-breaking field (SBF)
can be introduced by taking into account a classical electron current. The
ground state, in the limit of small nonlinearity, becomes a squeezed state, and
thus the modes become entangled. The smaller is the SBF, the greater is
entanglement. Superfluid-like behavior is observed in the study of entanglement
growth from an initial coherent state, since in the short-time range the growth
does not depend on the SBF amplitude, and on the initial state amplitude. On
the other hand, the latter is the only parameter which determines entanglement
in the absence of the SBF
The Mid-Infrared Spectral Energy Distribution, Surface Brightness and Color Profiles in Elliptical Galaxies
We describe photometry at mid-infrared passbands (1.2 - 24 microns) for a
sample of 18 elliptical galaxies. All surface brightness distributions resemble
de Vaucouleurs profiles, indicating that most of the emission arises from the
photospheres or circumstellar regions of red giant stars. The spectral energy
distribution peaks near 1.6 microns, but the half-light or effective radius has
a pronounced minimum near the K band (2.15 microns). Apart from the 24 micron
passband, all sample-averaged radial color profiles have measurable slopes
within about twice the (K band) effective radius. Evidently this variation
arises because of an increase in stellar metallicity toward the galactic cores.
For example, the sampled-averaged color profile (K - 5.8 microns) has a
positive slope although no obvious absorption feature is observed in spectra of
elliptical galaxies near 5.8 microns. This, and the minimum in the effective
radius, suggests that the K band may be anomalously luminous in metal-rich
stars in galaxy cores. Unusual radial color profiles involving the 24 micron
passband may suggest that some 24 micron emission comes from interstellar not
circumstellar dust grains.Comment: 18 pages. Accepted by Ap
Teleportation on a quantum dot array
We present a model of quantum teleportation protocol based on a double
quantum dot array. The unknown qubit is encoded using a pair of quantum dots,
coupled by tunneling, with one excess electron. It is shown how to create
maximally entangled states with this kind of qubits using an adiabatically
increasing Coulomb repulsion between different pairs. This entangled states are
exploited to perform teleportation again using an adiabatic coupling between
them and the incoming unknown state. Finally, a sudden separation of Bob's
qubit enables a time evolution of Alice's state providing a modified version of
standard Bell measurement. Substituting the four quantum dots entangled state
with a chain of coupled DQD's, a quantum channel with high fidelity arises from
this scheme allowing the transmission over long distances.Comment: 4 pages, 2 figure
Hot gaseous atmospheres in galaxy groups and clusters are both heated and cooled by X-ray cavities
Expanding X-ray cavities observed in hot gas atmospheres of many galaxy
groups and clusters generate shock waves and turbulence that are primary
heating mechanisms required to avoid uninhibited radiatively cooling flows
which are not observed. However, we show here that the evolution of buoyant
cavities also stimulates radiative cooling of observable masses of
low-temperature gas. During their early evolution, radiative cooling occurs in
the wakes of buoyant cavities in two locations: in thin radial filaments
parallel to the buoyant velocity and more broadly in gas compressed beneath
rising cavities. Radiation from these sustained compressions removes entropy
from the hot gas. Gas experiencing the largest entropy loss cools first,
followed by gas with progressively less entropy loss. Most cooling occurs at
late times, yrs, long after the X-ray cavities have disrupted
and are impossible to detect. During these late times, slightly denser low
entropy gas sinks slowly toward the centers of the hot atmospheres where it
cools intermittently, forming clouds near the cluster center. Single cavities
of energy ergs in the atmosphere of the NGC 5044 group create
of cooled gas, exceeding the mass of extended
molecular gas currently observed in that group. The cooled gas clouds we
compute share many attributes with molecular clouds recently observed in NGC
5044 with ALMA: self-gravitationally unbound, dust-free, quasi-randomly
distributed within a few kpc around the group center.Comment: 12 pages, 11 figure; accepted for publication by Ap
Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology
We calculate and display the primordial light-element abundances as a
function of a neutrino degeneracy parameter \xi common to all flavors. It is
the only unknown parameter characterizing the thermal medium at the primordial
nucleosynthesis epoch. The observed primordial helium abundance Y_p is the most
sensitive cosmic ``leptometer.'' Adopting the conservative Y_p error analysis
of Olive and Skillman implies -0.04 \alt \xi \alt 0.07 whereas the errors
stated by Izotov and Thuan imply \xi=0.0245+-0.0092 (1 sigma). Improved
determinations of the baryon abundance have no significant impact on this
situation. A determination of Y_p that reliably distinguishes between a
vanishing or nonvanishing \xi is a crucial test of the cosmological standard
assumption that sphaleron effects equilibrate the cosmic lepton and baryon
asymmetries.Comment: 5 pages, 2 figures; minor changes, references added, replaced to
match the published version in PRD (Brief Reports
Detecting Axion-Like Particles With Gamma Ray Telescopes
We propose that axion-like particles (ALPs) with a two-photon vertex,
consistent with all astrophysical and laboratory bounds, may lead to a
detectable signature in the spectra of high-energy gamma ray sources. This
occurs as a result of gamma rays being converted into ALPs in the magnetic
fields of efficient astrophysical accelerators according to the "Hillas
criterion", such as jets of active galactic nuclei or hot spots of radio
galaxies. The discovery of such an effect is possible by GLAST in the 1-100 GeV
range and by ground based gamma ray telescopes in the TeV range.Comment: corrected typos, one plot modified, material rearranged for
clarification. Conclusions unchanged. Matches version published in Phys. Rev.
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