In collaboration with theoretical quantum physicists from Pavia, Italy, we have studied minimum-energy quantum reading. Here in Quantum Optics Lab Olomouc we have demonstrated some efficient reading protocols using fiber-optics interferometric setup which encodes two quantum bits in which-way degree of freedom of photons employed. You can find details on the quantum reading protocols in the paper Experimental implementation of unambiguous quantum reading, Phys. Rev. A 85, 012308 (2012).
How many photons does it take to measure a transmittance? Sometimes less than one.