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

Why Europe is Not Carbon Competitive. Bruegel policy brief 2007/05, November 2007

Summary. Europe specialises more than its main global competitors in industries with relatively high carbon emissions, such as minerals and chemicals, rather than in high-tech industries and services . This would have a real effect on Europe’s competitiveness in a world regulated by carbon pricing schemes such as the EU’s Emissions Trading Scheme – even if other blocs apply them as the EU does. Furthermore, in the absence of fair and undistorting carbon pricing schemes worldwide, there is a real risk that business will resort to regulatory arbitrage which will entail a shift in where emissions take place – but no reduction in global emissions. In any case, the issue of which economies are ‘carbon competitive’ will gradually become a much bigger part of the global trade conversation

Some characterizations of Howson PC-groups

We show that in the class of partially commutative groups, the conditions of being Howson, being fully residually free, and being free product of free-abelian groups, are equivalent