Assuming the electrons are non interacting and spin degenerate, the conductance of a quasi one dimensional quantum wire is quantised in units of 2e^2/h. For small voltages, we simply count how many bands have their bottoms below the chemical potential and multiply this by 2e^2/h. This is due to...
Modelling the onset of decoherence in a subspace as a transition from this subspace
http://www.ba.infn.it/~pascazio/publications/sudarshan_seven_quests.pdf
(Section 10 is relevant)
I am currently reading papers discussing the Zeno Effect. The linked paper discusses modelling a transition out of...
http://arxiv.org/pdf/0903.3297v1.pdf
This paper discusses modelling a transition out of the wanted subspace as the onset of decoherence. I don't quite understand this model. Why does remaining in the subspace mean that coherence must be preserved? Surely environmental effects can decohere the...
http://arxiv.org/pdf/0903.3297v1.pdf
At the moment I'm not too concerned with the applications to Quantum Computation, rather the way in which general decoherence is prevented by restraining the system state to lie in a subspace.
I am currently reading papers discussing the Zeno Effect, which discuss how measuring a system at high frequencies can almost freeze the state of a system, or keep the system in a specific subspace of states. This can be easily seen using the projection postulate. Often the topic of decoherence...