Quantum probability law from ‘environment-assisted invariance’ in terms of pure-state twin unitaries
Fedor Herbut
Zurek's derivation of the Born rule from envariance (environment-assisted invariance) is retraced in an attempt to present a more detailed derivation, which is extended to encompass the trace-rule form of the quantum probability law in its full generality. The investigation begins by a review presentation of Schmidt decomposition, and a detailed and complete theory of twin unitaries, which are the other face of envariance, and which stand in close connection with twin observables. The trace rule tr( E ρ), with E being an event (projector) and ρ a quantum state (density operator), is derived in five stages. The first three achieve the same as Zurek's derivation of Born's rule, but in a different way, using the full power of twin unitaries. Stage 4 extends the Zurek-like derivation to states (ray projectors) that are not eigenstates of the density operator. Finally, stage 5 utilizes the assumption of continuity of the probability law in the density operators to extend the trace rule to isolated (not correlated) systems.
arXiv:quant-ph/0611220•Journal of Physics A Mathematical and Theoretical•May 14, 2007•14 citations