Fidelity of states in infinite dimensional quantum systems
  In this paper we discuss the fidelity of states in infinite dimensional systems, give an elementary proof of the infinite dimensional version of Uhlmann's theorem, and then, apply it to generalize several properties of the fidelity from finite dimensional case to infinite dimensional case. Some of them are somewhat different from those for finite dimensional case. 
Jinchuan Hou and Xiaofei Qi
quant-ph math.FA