We report preparation and characterization of coherent superposition states t |0> + alpha |1> of electromagnetic field by conditional measurements on a beamsplitter. The state is generated in one of the beam splitter output channels if a coherent state and a single-photon Fock state |1> are present in the two input ports and a single photon is registered in the other beam splitter output. The single photon thus plays a role of a "catalyst": it is explicitly present in both the input and the output channels of the interaction yet facilitates generation of a nonclassical state of light.
@article{arxiv.quant-ph/0202164,
title = {Quantum-optical catalysis: generating "Schroedinger kittens" by means of linear optics},
author = {A. I. Lvovsky and J. Mlynek},
journal= {arXiv preprint arXiv:quant-ph/0202164},
year = {2009}
}