74,950 research outputs found
Affine maps of density matrices
For quantum systems described by finite matrices, linear and affine maps of
matrices are shown to provide equivalent descriptions of evolution of density
matrices for a subsystem caused by unitary Hamiltonian evolution in a larger
system; an affine map can be replaced by a linear map, and a linear map can be
replaced by an affine map. There may be significant advantage in using an
affine map. The linear map is generally not completely positive, but the linear
part of an equivalent affine map can be chosen to be completely positive and
related in the simplest possible way to the unitary Hamiltonian evolution in
the larger system.Comment: 4 pages, title changed, sentence added, reference update
Remote sensing observatory validation of surface soil moisture using Advanced Microwave Scanning Radiometer E, Common Land Model, and ground based data: Case study in SMEX03 Little River Region, Georgia, U.S.
Optimal soil moisture estimation may be characterized by intercomparisons among remotely sensed measurements, groundâbased measurements, and land surface models. In this study, we compared soil moisture from Advanced Microwave Scanning Radiometer E (AMSRâE), groundâbased measurements, and a SoilâVegetationâAtmosphere Transfer (SVAT) model for the Soil Moisture Experiments in 2003 (SMEX03) Little River region, Georgia. The Common Land Model (CLM) reasonably replicated soil moisture patterns in dry down and wetting after rainfall though it had modest wet biases (0.001â0.054 m3/m3) as compared to AMSRâE and ground data. While the AMSRâE average soil moisture agreed well with the other data sources, it had extremely low temporal variability, especially during the growing season from May to October. The comparison results showed that highest mean absolute error (MAE) and root mean squared error (RMSE) were 0.054 and 0.059 m3/m3 for short and long periods, respectively. Even if CLM and AMSRâE had complementary strengths, low MAE (0.018â0.054 m3/m3) and RMSE (0.023â0.059 m3/m3) soil moisture errors for CLM and soil moisture low biases (0.003â0.031 m3/m3) for AMSRâE, care should be taken prior to employing AMSRâE retrieved soil moisture products directly for hydrological application due to its failure to replicate temporal variability. AMSRâE error characteristics identified in this study should be used to guide enhancement of retrieval algorithms and improve satellite observations for hydrological sciences
Necessary and sufficient conditions for bipartite entanglement
Necessary and sufficient conditions for bipartite entanglement are derived,
which apply to arbitrary Hilbert spaces. Motivated by the concept of witnesses,
optimized entanglement inequalities are formulated solely in terms of arbitrary
Hermitian operators, which makes them useful for applications in experiments.
The needed optimization procedure is based on a separability eigenvalue
problem, whose analytical solutions are derived for a special class of
projection operators. For general Hermitian operators, a numerical
implementation of entanglement tests is proposed. It is also shown how to
identify bound entangled states with positive partial transposition.Comment: 7 pages, 2 figur
A method to find quantum noiseless subsystems
We develop a structure theory for decoherence-free subspaces and noiseless
subsystems that applies to arbitrary (not necessarily unital) quantum
operations. The theory can be alternatively phrased in terms of the
superoperator perspective, or the algebraic noise commutant formalism. As an
application, we propose a method for finding all such subspaces and subsystems
for arbitrary quantum operations. We suggest that this work brings the
fundamental passive technique for error correction in quantum computing an
important step closer to practical realization.Comment: 5 pages, to appear in Physical Review Letter
On multipartite invariant states I. Unitary symmetry
We propose a natural generalization of bipartite Werner and isotropic states
to multipartite systems consisting of an arbitrary even number of d-dimensional
subsystems (qudits). These generalized states are invariant under the action of
local unitary operations. We study basic properties of multipartite invariant
states: separability criteria and multi-PPT conditions.Comment: 9 pages; slight correction
Identifying the Higgs Spin and Parity in Decays to Z Pairs
Higgs decays to Z boson pairs may be exploited to determine spin and parity
of the Higgs boson, a method complementary to spin-parity measurements in
Higgs-strahlung. For a Higgs mass above the on-shell ZZ decay threshold, a
model-independent analysis can be performed, but only by making use of
additional angular correlation effects in gluon-gluon fusion at the LHC and
gamma-gamma fusion at linear colliders. In the intermediate mass range, in
which the Higgs boson decays into pairs of real and virtual Z bosons, threshold
effects and angular correlations, parallel to Higgs-strahlung, may be adopted
to determine spin and parity, though high event rates will be required for the
analysis in practice.Comment: 14 pages, 2 postscript figure
Partial scaling transform of multiqubit states as a criterion of separability
The partial scaling transform of the density matrix for multiqubit states is
introduced to detect entanglement of quantum states. The transform contains
partial transposition as a special case. The scaling transform corresponds to
partial time scaling of subsystem (or partial Planck's constant scaling) which
was used to formulate recently separability criterion for continous variables.A
measure of entanglement which is a generalization of negativity measure is
introduced being based on tomographic probability description of spin states.Comment: 16 pages, 5 figures, submitted to J. Phys. A: Math. Ge
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