Generating photon-added states without adding a photon

Optical Parametric Amplifiers convert pump photons to pairs of signal and idler photons. In this work, we demonstrate that a continuous range of non-classical states, including a displaced number state and photon-added state, can be prepared in the signal when the input idler mode contains a pure single-photon state and the output idler mode is post-selected to be unchanged by the OPA, depending on the gain of the OPA. The ability to continuously tune the gain and hence the non-classical states provide an advantage over a similar approach for conventional beam splitter with fixed reflectivity.
Reference
S. U. Shringarpure and J. D. Franson, "Generating photon-added states without adding a photon," Physical Review A 100 (4) 043802 (2019).