545 research outputs found
Entangling power and operator entanglement in qudit systems
We establish the entangling power of a unitary operator on a general
finite-dimensional bipartite quantum system with and without ancillas, and give
relations between the entangling power based on the von Neumann entropy and the
entangling power based on the linear entropy. Significantly, we demonstrate
that the entangling power of a general controlled unitary operator acting on
two equal-dimensional qudits is proportional to the corresponding operator
entanglement if linear entropy is adopted as the quantity representing the
degree of entanglement. We discuss the entangling power and operator
entanglement of three representative quantum gates on qudits: the SUM, double
SUM, and SWAP gates.Comment: 8 pages, 1 figure. Version 3: Figure was improved and the MS was a
bit shortene
CFT driven cosmology and the DGP/CFT correspondence
We present a dual 5D braneworld picture of a recently suggested model for a
microcanonical description of a 4D cosmology driven by a conformal field theory
with a large number of quantum fields. The 5D side of the duality relation is
represented by a generalized brane induced gravity model in a Schwarzschild-de
Sitter bulk. The values of the bulk cosmological and the induced 4D
cosmological constants are determined by requiring the absence of conical
singularity at the de Sitter horizon of the Euclidean Schwarzschild-de Sitter
bulk. Those values belong to the vicinity of the upper bound of a range of
admissible values for the cosmological constant. This upper bound is enforced
by the 4D CFT and coincides with the natural gravitational cutoff in a theory
with many quantum species. The resulting DGP/CFT duality suggests the
possibility of a new type of {\em background independent} correspondence. A
mechanism for inverting the sign of the effective cosmological constant is
found, which might reconcile a negative value of the primordial cosmological
constant compatible with supersymmetry with the one required by inflationary
cosmology.Comment: LaTeX, 23 pages, 3 figure
On the practicality of time-optimal two-qubit Hamiltonian simulation
What is the time-optimal way of using a set of control Hamiltonians to obtain
a desired interaction? Vidal, Hammerer and Cirac [Phys. Rev. Lett. 88 (2002)
237902] have obtained a set of powerful results characterizing the time-optimal
simulation of a two-qubit quantum gate using a fixed interaction Hamiltonian
and fast local control over the individual qubits. How practically useful are
these results? We prove that there are two-qubit Hamiltonians such that
time-optimal simulation requires infinitely many steps of evolution, each
infinitesimally small, and thus is physically impractical. A procedure is given
to determine which two-qubit Hamiltonians have this property, and we show that
almost all Hamiltonians do. Finally, we determine some bounds on the penalty
that must be paid in the simulation time if the number of steps is fixed at a
finite number, and show that the cost in simulation time is not too great.Comment: 9 pages, 2 figure
Randall-Sundrum Brane Tensions
We show that the singular sources in the energy-momentum tensor for the
Randall-Sundrum brane world, viewed as a solution of type IIB supergravity, are
composed of two elements. One of these is a D3-brane source with tension
opposite in sign to the RS tension in five dimensions; the other arises from
patching two regions of flat ten-dimensional spacetime. This resolves an
apparent discrepancy between supersymmetry and the sign and magnitude of the RS
tension.Comment: Latex, 21 pages, 2 figure
Ground--state energies and widths of He and Li
We extract energies and widths of the ground states of He and Li from
recent single--level R--matrix fits to the spectra of the H)He and the He)Li reactions. The widths
obtained differ significantly from the formal R--matrix values but they are
close to those measured as full widths at half maxima of the spectra in various
experiments. The energies are somewhat lower than those given by usual
estimates of the peak positions. The extracted values are close to the
S--matrix poles calculated previously from the multi--term analyses of the
N-He elastic scattering data.Comment: 3 pages, no figures, uses revtex.sty, accepted for publication in
PRC, uuencoded postscript and tex-files available at
ftp://is1.kph.tuwien.ac.at/pub/ohu/fwidth.u
Counterterms and dual holographic anomalies in CS gravity
The holographic Weyl anomaly associated to Chern-Simons gravity in 2n+1
dimensions is proportional to the Euler term in 2n dimensions, with no
contributions from the Weyl tensor. We compute the holographic energy-momentum
tensor associated to Chern-Simons gravity directly from the action, in an
arbitrary odd-dimensional spacetime. We show, in particular, that the
counterterms rendering the action finite contain only terms of the Lovelock
type.Comment: 10 pages, no figure
THE MASS-RADIUS RELATION OF YOUNG STARS. I. USCO 5, AN M4.5 ECLIPSING BINARY IN UPPER SCORPIUS OBSERVED BY K2
We present the discovery that UScoCTIO 5, a known spectroscopic binary in the Upper Scorpius star-forming region (P = 34 days, Mtot sin(i) = 0.64 Mâ), is an eclipsing system with both primary and secondary eclipses apparent in K2 light curves obtained during Campaign 2. We have simultaneously fit the eclipse profiles from the K2 light curves and the existing RV data to demonstrate that UScoCTIO 5 consists of a pair of nearly identical M4.5 stars with MA = 0.329 ± 0.002 Mâ, RA = 0.834 ± 0.006 Râ, MB = 0.317 ± 0.002 Mâ, and RB = 0.810 ± 0.006 Râ. The radii are broadly consistent with pre-main-sequence ages predicted by stellar evolutionary models, but none agree to within the uncertainties. All models predict systematically incorrect masses at the 25%-50% level for the HR diagram position of these mid-M dwarfs, suggesting significant modifications to mass-dependent outcomes of star and planet formation. The form of the discrepancy for most model sets is not that they predict luminosities that are too low, but rather that they predict temperatures that are too high, suggesting that the models do not fully encompass the physics of energy transport (via convection and/or missing opacities) and/or a miscalibration of the SpT-Teff scale. The simplest modification to the models (changing Teff to match observations) would yield an older age for this system, in line with the recently proposed older age of Upper Scorpius (Ï âŒ 11 Myr)
A fixed-point property of logic-based bargaining solution
Abstract. This paper presents a logic-based bargaining solution based on Zhang and Zhangâs framework. It is shown that if the demand sets of players are logically closed, the solution satisfies a fixed-point property, which says that the outcome of bargaining is the result of mutual belief revision. The result is interesting not only because it presents a desirable logical property of bargaining solution but also establishes a link between bargaining theory and multi-agent belief revision.
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