14,056 research outputs found
Efficient least-squares basket-weaving
We report on a novel method to solve the basket-weaving problem.
Basket-weaving is a technique that is used to remove scan-line patterns from
single-dish radio maps. The new approach applies linear least-squares and works
on gridded maps from arbitrarily sampled data, which greatly improves
computational efficiency and robustness. It also allows masking of bad data,
which is useful for cases where radio frequency interference is present in the
data. We evaluate the algorithms using simulations and real data obtained with
the Effelsberg 100-m telescope.Comment: 11 pages, 11 figures, accepted by A&
Simple Derivation of the Lindblad Equation
The Lindblad equation is an evolution equation for the density matrix in
quantum theory. It is the general linear, Markovian, form which ensures that
the density matrix is hermitian, trace 1, positive and completely positive.
Some elementary examples of the Lindblad equation are given. The derivation of
the Lindblad equation presented here is "simple" in that all it uses is the
expression of a hermitian matrix in terms of its orthonormal eigenvectors and
real eigenvalues. Thus, it is appropriate for students who have learned the
algebra of quantum theory. Where helpful, arguments are first given in a
two-dimensional hilbert space.Comment: To be published in the European Journal of Physic
Local unitary equivalence and entanglement of multipartite pure states
The necessary and sufficient conditions for the equivalence of arbitrary
n-qubit pure quantum states under Local Unitary (LU) operations derived in [B.
Kraus Phys. Rev. Lett. 104, 020504 (2010)] are used to determine the different
LU-equivalence classes of up to five-qubit states. Due to this classification
new parameters characterizing multipartite entanglement are found and their
physical interpretation is given. Moreover, the method is used to derive
examples of two n-qubit states (with n>2 arbitrary) which have the properties
that all the entropies of any subsystem coincide, however, the states are
neither LU-equivalent nor can be mapped into each other by general local
operations and classical communication
Local unitary equivalence of multipartite pure states
Necessary and sufficient conditions for the equivalence of arbitrary n-qubit
pure quantum states under Local Unitary (LU) operations are derived. First, an
easily computable standard form for multipartite states is introduced. Two
generic states are shown to be LU-equivalent iff their standard forms coincide.
The LU-equivalence problem for non--generic states is solved by presenting a
systematic method to determine the LU operators (if they exist) which
interconvert the two states.Comment: 5 page
Numerical Analysis of the Capacities for Two-Qubit Unitary Operations
We present numerical results on the capacities of two-qubit unitary
operations for creating entanglement and increasing the Holevo information of
an ensemble. In all cases tested, the maximum values calculated for the
capacities based on the Holevo information are close to the capacities based on
the entanglement. This indicates that the capacities based on the Holevo
information, which are very difficult to calculate, may be estimated from the
capacities based upon the entanglement, which are relatively straightforward to
calculate.Comment: 9 pages, 10 figure
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