25,361 research outputs found
Lick Slit Spectra of Thirty-Eight Objective Prism QSO Candidates and Low Metallicity Halo Stars
We present Lick Observatory slit spectra of 38 objects which were claimed to
have pronounced ultraviolet excess and emission lines by Zhan \& Chen. Most of
our spectra have FWHM spectral resolutions of about 4~\AA , and relatively high
S/N of about 10 -- 50, although some have FWHM ~\AA ~or lower S/N.
We find eleven QSOs, four galaxies at , twenty-two stars and one
unidentified object with a low S/N spectrum. Six of the QSOs show absorption
systems, including Q0000+027A with a relatively strong associated C~IV
absorption system, and Q0008+008 (V) with a damped Ly
system with an H~I column density of cm. The stars include a
wide variety of spectral types. There is one new DA4 white dwarf at 170~pc, one
sdB at 14~kpc, and three M stars. The rest are of types F, G and K. We have
measured the equivalent widths of the Ca~II~K line, the G-band and the Balmer
lines in ten stars with the best spectra, and we derive metallicities. Seven of
them are in the range ~[Fe/H]~, while the others are less
metal poor. If the stars are dwarfs, then they are at distances of 1 to 7~kpc,
but if they are giants, typical distances will be about 10~kpc.Comment: (Plain Tex, 21 pages, including tables. Send email to
'travell_oir%[email protected]' for 12 pages of figures) To appear in the
%%Astronomical Journal, August, 199
Threshold Error Penalty for Fault Tolerant Computation with Nearest Neighbour Communication
The error threshold for fault tolerant quantum computation with concatenated
encoding of qubits is penalized by internal communication overhead. Many
quantum computation proposals rely on nearest-neighbour communication, which
requires excess gate operations. For a qubit stripe with a width of L+1
physical qubits implementing L levels of concatenation, we find that the error
threshold of 2.1x10^-5 without any communication burden is reduced to 1.2x10^-7
when gate errors are the dominant source of error. This ~175X penalty in error
threshold translates to an ~13X penalty in the amplitude and timing of gate
operation control pulses.Comment: minor correctio
Measurement of Positronium hyperfine splitting with quantum oscillation
Interference between different energy eigenstates in a quantum system results
in an oscillation with a frequency which is proportional to the difference in
energy between the states. Such an oscillation is observable in polarized
positronium when it is placed in a magnetic field. In order to measure the
hyperfine splitting of positronium, we perform the precise measurement of this
oscillation using a high quality superconducting magnet and fast
photon-detectors. A result of ~GHz is obtained which is consistent with both theoretical
calculations and previous precise measurements.Comment: 4 figures accepted by Phys. Lett.
Generalized W-Class State and its Monogamy Relation
We generalize the W class of states from qubits to qudits and prove
that their entanglement is fully characterized by their partial entanglements
even for the case of the mixture that consists of a W-class state and a product
state .Comment: 12 pages, 1 figur
High Temperature Macroscopic Entanglement
In this paper I intend to show that macroscopic entanglement is possible at
high temperatures. I analyze multipartite entanglement produced by the
pairing mechanism which features strongly in the fermionic lattice models of
high superconductivity. This problem is shown to be equivalent to
calculating multipartite entanglement in totally symmetric states of qubits. I
demonstrate that we can conclusively calculate the relative entropy of
entanglement within any subset of qubits in an overall symmetric state. Three
main results then follow. First, I show that the condition for
superconductivity, namely the existence of the off diagonal long range order
(ODLRO), is not dependent on two-site entanglement, but on just classical
correlations as the sites become more and more distant. Secondly, the
entanglement that does survive in the thermodynamical limit is the entanglement
of the total lattice and, at half filling, it scales with the log of the number
of sites. It is this entanglement that will exist at temperatures below the
superconducting critical temperature, which can currently be as high as 160
Kelvin. Thirdly, I prove that a complete mixture of symmetric states does not
contain any entanglement in the macroscopic limit. On the other hand, the same
mixture of symmetric states possesses the same two qubit entanglement features
as the pure states involved, in the sense that the mixing does not destroy
entanglement for finite number of qubits, albeit it does decrease it. Maximal
mixing of symmetric states also does not destroy ODLRO and classical
correlations. I discuss various other inequalities between different
entanglements as well as generalizations to the subsystems of any
dimensionality (i.e. higher than spin half).Comment: 14 pages, no figure
On the Phase Covariant Quantum Cloning
It is known that in phase covariant quantum cloning the equatorial states on
the Bloch sphere can be cloned with a fidelity higher than the optimal bound
established for universal quantum cloning. We generalize this concept to
include other states on the Bloch sphere with a definite component of spin.
It is shown that once we know the component, we can always clone a state
with a fidelity higher than the universal value and that of equatorial states.
We also make a detailed study of the entanglement properties of the output
copies and show that the equatorial states are the only states which give rise
to separable density matrix for the outputs.Comment: Revtex4, 6 pages, 5 eps figure
From AKNS to derivative NLS hierarchies via deformations of associative products
Using deformations of associative products, derivative nonlinear Schrodinger
(DNLS) hierarchies are recovered as AKNS-type hierarchies. Since the latter can
also be formulated as Gelfand-Dickey-type Lax hierarchies, a recently developed
method to obtain 'functional representations' can be applied. We actually
consider hierarchies with dependent variables in any (possibly noncommutative)
associative algebra, e.g., an algebra of matrices of functions. This also
covers the case of hierarchies of coupled DNLS equations.Comment: 22 pages, 2nd version: title changed and material organized in a
different way, 3rd version: introduction and first part of section 2
rewritten, taking account of previously overlooked references. To appear in
J. Physics A: Math. Ge
Observation of kink instability during small B5.0 solar flare on 04 June, 2007
Using multi-wavelength observations of SoHO/MDI, SOT-Hinode/blue-continuum
(4504 \AA), G-band (4305 \AA), Ca II H (3968 \AA) and TRACE 171 \AA, we present
the observational signature of highly twisted magnetic loop in AR 10960 during
the period 04:43 UT-04:52 UT at 4 June, 2007. SOT-Hinode/blue-continuum (4504
\AA) observations show that penumbral filaments of positive polarity sunspot
have counter-clock wise twist, which may be caused by the clock-wise rotation
of the spot umbrae. The coronal loop, whose one footpoint is anchored in this
sunspot, shows strong right-handed twist in chromospheric SOT-Hinode/Ca II H
(3968 \AA) and coronal TRACE 171 \AA\, images. The length and the radius of the
loop are 80 Mm and 4.0 Mm respectively. The distance between
neighboring turns of magnetic field lines (i.e. pitch) is estimated as
10 Mm. The total twist angle, 12 (estimated for the
homogeneous distribution of the twist along the loop), is much larger than the
Kruskal -Shafranov instability criterion. We detected clear double structure of
the loop top during 04:47-04:51 UT on TRACE 171 \AA \ images, which is
consistent with simulated kink instability in curved coronal loops
(T{\"o}r{\"o}k et al. 2004). We suggest, that the kink instability of this
twisted magnetic loop triggered B5.0 class solar flare, which occurred between
04:40 UT and 04:51 UT in this active region.Comment: 24 pages, 5 Figures; The Astrophysical Journa
Phase-covariant quantum cloning of qudits
We study the phase-covariant quantum cloning machine for qudits, i.e. the
input states in d-level quantum system have complex coefficients with arbitrary
phase but constant module. A cloning unitary transformation is proposed. After
optimizing the fidelity between input state and single qudit reduced density
opertor of output state, we obtain the optimal fidelity for 1 to 2
phase-covariant quantum cloning of qudits and the corresponding cloning
transformation.Comment: Revtex, 6 page
A geometrically motivated coordinate system for exploring spacetime dynamics in numerical-relativity simulations using a quasi-Kinnersley tetrad
We investigate the suitability and properties of a quasi-Kinnersley tetrad
and a geometrically motivated coordinate system as tools for quantifying both
strong-field and wave-zone effects in numerical relativity (NR) simulations. We
fix the radial and latitudinal coordinate degrees of freedom of the metric,
using the Coulomb potential associated with the quasi-Kinnersley transverse
frame. These coordinates are invariants of the spacetime and can be used to
unambiguously fix the outstanding spin-boost freedom associated with the
quasi-Kinnersley frame (resulting in a preferred quasi-Kinnersley tetrad
(QKT)). In the limit of small perturbations about a Kerr spacetime, these
coordinates and QKT reduce to Boyer-Lindquist coordinates and the Kinnersley
tetrad, irrespective of the simulation gauge choice. We explore the properties
of this construction both analytically and numerically, and we gain insights
regarding the propagation of radiation described by a super-Poynting vector. We
also quantify in detail the peeling properties of the chosen tetrad and gauge.
We argue that these choices are particularly well suited for a rapidly
converging wave-extraction algorithm as the extraction location approaches
infinity, and we explore numerically the extent to which this property remains
applicable on the interior of a computational domain. Using a number of
additional tests, we verify that the prescription behaves as required in the
appropriate limits regardless of simulation gauge. We explore the behavior of
the geometrically motivated coordinate system in dynamical binary-black-hole NR
mergers, and find them useful for visualizing features in NR simulations such
as the spurious "junk" radiation. Finally, we carefully scrutinize the head-on
collision of two black holes and, for example, the way in which the extracted
waveform changes as it moves through the computational domain.Comment: 30 pages, 17 figures, 2 table
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