Tradeoff between energy and error in the discrimination of   quantum-optical devices
  We address the problem of energy-error tradeoff in the discrimination between two linear passive quantum optical devices with a single use. We provide an analytical derivation of the optimal strategy for beamsplitters and an iterative algorithm converging to the optimum in the general case. We then compare the optimal strategy with a simpler strategy using coherent input states and homodyne detection. It turns out that the former requires much less energy in order to achieve the same performances. 
Alessandro Bisio, Michele Dall'Arno, Giacomo Mauro D'Ariano
quant-ph