4,134 research outputs found
Fibrations and stable generalized complex structures
A generalized complex structure is called stable if its defining
anticanonical section vanishes transversally, on a codimension-two submanifold.
Alternatively, it is a zero elliptic residue symplectic structure in the
elliptic tangent bundle associated to this submanifold. We develop
Gompf-Thurston symplectic techniques adapted to Lie algebroids, and use these
to construct stable generalized complex structures out of log-symplectic
structures. In particular we introduce the notion of a boundary Lefschetz
fibration for this purpose and describe how they can be obtained from genus one
Lefschetz fibrations over the disk.Comment: 35 pages, 2 figure
Classification of boundary Lefschetz fibrations over the disc
We show that a four-manifold admits a boundary Lefschetz fibration over the
disc if and only if it is diffeomorphic to ,
or . Given the relation between boundary Lefschetz
fibrations and stable generalized complex structures, we conclude that the
manifolds , and admit stable
structures whose type change locus has a single component and are the only
four-manifolds whose stable structure arise from boundary Lefschetz fibrations
over the disc.Comment: 18 pages, 8 figures. Paper for the proceedings of the conference in
honour of Prof. Nigel Hitchin on the occasion of his 70th birthda
Radiometric correction of LANDSAT data
The author has identified the following significant results. The six independent sensors of the multispectral band scanner are supposed to be identical; however, in actual practice, they may have different gain settings and offset factors, which result in the effect known as stripping (black lines at regular intervals) of the imagery. A simple two parameter method to correct the gain settings and offset factors of each of the sensors with respect to one sensor, taken as reference, was developed. This method assumes: (1) the response of a detector varies linearly with the radiance of radiation received, and (2) the means, as well as the standard deviations, of a reasonably large number of pixels, in a given wavelength band, are equal for each of the detectors for the radiometrically corrected data
Scaling laws for the decay of multiqubit entanglement
We investigate the decay of entanglement of generalized N-particle
Greenberger-Horne-Zeilinger (GHZ) states interacting with independent
reservoirs. Scaling laws for the decay of entanglement and for its finite-time
extinction (sudden death) are derived for different types of reservoirs. The
latter is found to increase with the number of particles. However, entanglement
becomes arbitrarily small, and therefore useless as a resource, much before it
completely disappears, around a time which is inversely proportional to the
number of particles. We also show that the decay of multi-particle GHZ states
can generate bound entangled states.Comment: Minor mistakes correcte
Tomographic Characterization of Three-Qubit Pure States with Only Two-Qubit Detectors
A tomographic process for three-qubit pure states using only pairwise
detections is presented.Comment: 3 pages; revtex4; v2: the focus on tomography was emphasized and the
experimental procedure detailed; v3: the text was improved in clarity, some
mistakes were correcte
Multipartite fully-nonlocal quantum states
We present a general method to characterize the quantum correlations obtained
after local measurements on multipartite systems. Sufficient conditions for a
quantum system to be fully-nonlocal according to a given partition, as well as
being (genuinely) multipartite fully-nonlocal, are derived. These conditions
allow us to identify all completely-connected graph states as multipartite
fully-nonlocal quantum states. Moreover, we show that this feature can also be
observed in mixed states: the tensor product of five copies of the Smolin
state, a biseparable and bound entangled state, is multipartite fully-nonlocal.Comment: 5 pages, 1 figure. Version published in PRA. Note that it does not
contain all the results from the previous version; these will be included in
a later, more general, pape
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