A positive formalism for quantum theory in the general boundary   formulation
  We introduce a new "positive formalism" for encoding quantum theories in the general boundary formulation, somewhat analogous to the mixed state formalism of the standard formulation. This makes the probability interpretation more natural and elegant, eliminates operationally irrelevant structure and opens the general boundary formulation to quantum information theory. 
Robert Oeckl (CCM-UNAM)
quant-ph gr-qc hep-th math-ph math.MP