37,398 research outputs found
Measurement in control and discrimination of entangled pairs under self-distortion
Quantum correlations and entanglement are fundamental resources for quantum
information and quantum communication processes. Developments in these fields
normally assume these resources stable and not susceptible of distortion. That
is not always the case, Heisenberg interactions between qubits can produce
distortion on entangled pairs generated for engineering purposes (e. g. for
quantum computation or quantum cryptography). Experimental work shows how to
produce entangled spin qubits in quantum dots and electron gases, so its
identification and control are crucial for later applications. The presence of
parasite magnetic fields modifies the expected properties and behavior for
which the pair was intended. Quantum measurement and control help to
discriminate the original state in order to correct it or, just to try of
reconstruct it using some procedures which do not alter their quantum nature.
Two different kinds of quantum entangled pairs driven by a Heisenberg
Hamiltonian with an additional inhomogeneous magnetic field which becoming
self-distorted, can be reconstructed without previous discrimination by adding
an external magnetic field, with fidelity close to 1 (with respect to the
original state, but without discrimination). After, each state can be more
efficiently discriminated. The aim of this work is to show how combining both
processes, first reconstruction without discrimination and after discrimination
with adequate non-local measurements, it's possible a) improve the
discrimination, and b) reprepare faithfully the original states. The complete
process gives fidelities better than 0.9. In the meanwhile, some results about
a class of equivalence for the required measurements were found. This property
lets us select the adequate measurement in order to ease the repreparation
after of discrimination, without loss of entanglement.Comment: 6 figure
The Critical Point of Unoriented Random Surfaces with a Non-Even Potential
The discrete model of the real symmetric one-matrix ensemble is analyzed with
a cubic interaction. The partition function is found to satisfy a recursion
relation that solves the model. The double-scaling limit of the recursion
relation leads to a Miura transformation relating the contributions to the free
energy coming from oriented and unoriented random surfaces. This transformation
is the same kind as found with a cuartic interaction.Comment: 20p (Frontpage included
The stellar population and the evolutionary state of HII regions and starburst galaxies
RHII and starbursts are both powered by massive stars. They are the main
contributors to the heating of the ISM via radiative and mechanical energy.
Techniques to derive the stellar content and the evolutionary state of RHIIs
and starbursts from their ultraviolet and optical integrated light are
reviewed. A prototypical RHII (NGC 604) and nuclear starburst (NGC 7714) are
discussed in more detail. The results reveal the necessity of multiwavelength
analyses of these objects to estimate their stellar content and their
evolutionary state in a consistent way.Comment: Proceedings of the JENAM Conference (Toulouse, September 1999). To be
published in New Astronomy Reviews, Editors Daniel Schaerer and Rosa Gonzalez
Delgado. 12 pages, 7 figure
Single-Step Distillation Protocol with Generalized Beam Splitters
We develop a distillation protocol for multilevel qubits (qudits) using
generalized beam splitters like in the proposal of Pan et al. for ordinary
qubits. We find an acceleration with respect to the scheme of Bennet et al.
when extended to qudits. It is also possible to distill entangled pairs of
photons carrying orbital angular momenta (OAM) states that conserves the total
angular momenta as those produced in recent experiments.Comment: REVTEX4 file, color figure
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