A limit formula for the quantum fidelity
  Quantum fidelity is a central tool in quantum information, quantifying how much two quantum states are similar. Here we propose a limit formula for the quantum fidelity between a mixed state and a pure state. As an example of an application, we apply this formula to the case of multimode Gaussian states, achieving a simple expression in terms of their first and second-order statistical moments. 
Gaetana Spedalieri, Christian Weedbrook, Stefano Pirandola
quant-ph cond-mat.other math-ph math.MP physics.optics