356,138 research outputs found
Method for classifying multiqubit states via the rank of the coefficient matrix and its application to four-qubit states
We construct coefficient matrices of size 2^l by 2^{n-l} associated with pure
n-qubit states and prove the invariance of the ranks of the coefficient
matrices under stochastic local operations and classical communication (SLOCC).
The ranks give rise to a simple way of partitioning pure n-qubit states into
inequivalent families and distinguishing degenerate families from one another
under SLOCC. Moreover, the classification scheme via the ranks of coefficient
matrices can be combined with other schemes to build a more refined
classification scheme. To exemplify we classify the nine families of four
qubits introduced by Verstraete et al. [Phys. Rev. A 65, 052112 (2002)] further
into inequivalent subfamilies via the ranks of coefficient matrices, and as a
result, we find 28 genuinely entangled families and all the degenerate classes
can be distinguished up to permutations of the four qubits. We also discuss the
completeness of the classification of four qubits into nine families
Disk Accretion onto Magnetized Neutron Stars: The Inner Disk Radius and Fastness Parameter
It is well known that the accretion disk around a magnetized compact star can
penetrate inside the magnetospheric boundary, so the magnetospheric radius
\ro does not represent the true inner edge \rin of the disk; but
controversies exist in the literature concerning the relation between \ro and
\rin. In the model of Ghosh & Lamb, the width of the boundary layer is given
by \delta=\ro-\rin\ll\ro, or \rin\simeq\ro, while Li & Wickramasinghe
recently argued that \rin could be significantly smaller than \ro in the
case of a slow rotator. Here we show that if the star is able to absorb the
angular momentum of disk plasma at \ro, appropriate for binary X-ray pulsars,
the inner disk radius can be constrained by 0.8\lsim \rin/\ro\lsim 1, and the
star reaches spin equilibrium with a relatively large value of the fastness
parameter (). For accreting neutron stars in low-mass X-ray
binaries (LMXBs), \ro is generally close to the stellar radius \rs so that
the toroidal field cannot transfer the spin-up torque efficiently to the star.
In this case the critical fastness parameter becomes smaller, but \rin is
still near \ro.Comment: 7 pages, 2 figures, to appear in Ap
Thiadizoloquinoxaline-Based Low-Bandgap Conjugated Polymers as Ambipolar Semiconductors for Organic Field Effect Transistors
Theory of the vortex matter transformations in high Tc superconductor YBCO
Flux line lattice in type II superconductors undergoes a transition into a
"disordered" phase like vortex liquid or vortex glass, due to thermal
fluctuations and random quenched disorder. We quantitatively describe the
competition between the thermal fluctuations and the disorder using the
Ginzburg -- Landau approach. The following T-H phase diagram of YBCO emerges.
There are just two distinct thermodynamical phases, the homogeneous and the
crystalline one, separated by a single first order transitions line. The line
however makes a wiggle near the experimentally claimed critical point at 12T.
The "critical point" is reinterpreted as a (noncritical) Kauzmann point in
which the latent heat vanishes and the line is parallel to the T axis. The
magnetization, the entropy and the specific heat discontinuities at melting
compare well with experiments.Comment: 4 pages 3 figure
Baryon enhancement in high-density QCD and relativistic heavy ion collisions
We argue that the collinear factorization of the fragmentation functions in
high energy nuclear collisions breaks down at transverse momenta due to high parton densities in the colliding hadrons and/or nuclei. We
find that gluon recombination dominates in that region. We calculate the
inclusive cross-section for meson and nucleon production using the low
energy theorems for the scale anomaly in QCD, and compare our quantitative
baryon-to-meson ratio to the RHIC data.Comment: 4 pages, 2 figure; Contribution to Quark Matter 2008 in Jaipur,
India; submitted to J. Phys.
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