Generation of large-amplitude coherent-state superposition via   ancilla-assisted photon-subtraction
  We propose and demonstrate a novel method to generate a large-amplitude coherent-state superposition (CSS) via ancilla-assisted photon-subtraction. The ancillary mode induces quantum interference of indistinguishable processes, widening the controllability of quantum superposition at the conditional output. We demonstrate the concept in the time domain, by a simple time-separated two-photon subtraction from cw squeezed light. We observe the largest CSS ever reported without any corrections, which will enable various quantum information applications with CSS states. 
Hiroki Takahashi, Kentaro Wakui, Shigenari Suzuki, Masahiro Takeoka,   Kazuhiro Hayasaka, Akira Furusawa, Masahide Sasaki