Photon Added Coherent States: Nondeterministic, Noiseless Amplification   in Quantum Metrology
  Probabilistic amplification through photon addition, at the output of an Mach-Zehnder interferometer is discussed for a coherent input state. When a metric of signal to noise ratio is considered, nondeterministic, noiseless amplification of a coherent state shows improvement over a standard coherent state, for the general addition of $m$ photons. The efficiency of realizable implementation of photon addition is also considered and shows how the collected statistics of a post selected state, depend on this efficiency. We also consider the effects of photon loss and inefficient detectors. 
Bryan T. Gard, Dong Li, Chenglong You, Kaushik P. Seshadreesan,   Richard Birrittella, Jerome Luine, Seyed Mohammad Hashemi ...
quant-ph