1,824 research outputs found
A study of separability criteria for mixed three-qubit states
We study the noisy GHZ-W mixture. We demonstrate some necessary but not
sufficient criteria for different classes of separability of these states. It
turns out that the partial transposition criterion of Peres and the criteria of
G\"uhne and Seevinck dealing with matrix elements are the strongest ones for
different separability classes of this 2 parameter state. As a new result we
determine a set of entangled states of positive partial transpose.Comment: 18 pages, 10 figures, PRA styl
The attractor mechanism as a distillation procedure
In a recent paper it has been shown that for double extremal static
spherically symmetric BPS black hole solutions in the STU model the well-known
process of moduli stabilization at the horizon can be recast in a form of a
distillation procedure of a three-qubit entangled state of GHZ-type. By
studying the full flow in moduli space in this paper we investigate this
distillation procedure in more detail. We introduce a three-qubit state with
amplitudes depending on the conserved charges the warp factor, and the moduli.
We show that for the recently discovered non-BPS solutions it is possible to
see how the distillation procedure unfolds itself as we approach the horizon.
For the non-BPS seed solutions at the asymptotically Minkowski region we are
starting with a three-qubit state having seven nonequal nonvanishing amplitudes
and finally at the horizon we get a GHZ state with merely four nonvanishing
ones with equal magnitudes. The magnitude of the surviving nonvanishing
amplitudes is proportional to the macroscopic black hole entropy. A systematic
study of such attractor states shows that their properties reflect the
structure of the fake superpotential. We also demonstrate that when starting
with the very special values for the moduli corresponding to flat directions
the uniform structure at the horizon deteriorates due to errors generalizing
the usual bit flips acting on the qubits of the attractor states.Comment: 38 pages LaTe
The Evolution of the Global Star Formation History as Measured from the Hubble Deep Field
The Hubble Deep Field (HDF) is the deepest set of multicolor optical
photometric observations ever undertaken, and offers a valuable data set with
which to study galaxy evolution. Combining the optical WFPC2 data with
ground-based near-infrared photometry, we derive photometrically estimated
redshifts for HDF galaxies with J<23.5. We demonstrate that incorporating the
near-infrared data reduces the uncertainty in the estimated redshifts by
approximately 40% and is required to remove systematic uncertainties within the
redshift range 1<z<2. Utilizing these photometric redshifts, we determine the
evolution of the comoving ultraviolet (2800 A) luminosity density (presumed to
be proportional to the global star formation rate) from a redshift of z=0.5 to
z=2. We find that the global star formation rate increases rapidly with
redshift, rising by a factor of 12 from a redshift of zero to a peak at z~1.5.
For redshifts beyond 1.5, it decreases monotonically. Our measures of the star
formation rate are consistent with those found by Lilly et al. (1996) from the
CFRS at z 2, and
bridge the redshift gap between those two samples. The overall star formation
or metal enrichment rate history is consistent with the predictions of Pei and
Fall (1995) based on the evolving HI content of Lyman-alpha QSO absorption line
systems.Comment: Latex format, 10 pages, 3 postscript figures. Accepted for
publication in Ap J Letter
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