Linear-Optical Processing Cannot Increase Photon Efficiency

D. W. Berry, A. I. Lvovsky
2010 Physical Review Letters  
We answer the question whether linear-optical processing of the states produced by one or multiple imperfect single-photon sources can improve the single-photon fidelity. This processing can include arbitrary interferometers, coherent states, feedforward, and conditioning on results of detections. We show that without introducing multiphoton components, the single-photon fraction in any of the single-mode states resulting from such processing cannot be made to exceed the efficiency of the best
more » ... ciency of the best available photon source. If multiphoton components are allowed, the single-photon fidelity cannot be increased beyond 1/2. We propose a natural general definition of the quantum-optical state efficiency, and show that it cannot increase under linear-optical processing.
doi:10.1103/physrevlett.105.203601 pmid:21231232 fatcat:shjs2qcaczdrpo2b3wxh6lnj7q