Generating entangled superpositions of macroscopically distinguishable states within a parametric oscillator

We suggest a variant of the recently proposed experiment for the generation of a kind of mesoscopic superposition quantum state (a Schrödinger-cat-type state), using two coupled parametric down-converter nonlinear crystals [F. De Martini, Phys. Rev. Lett. 81, 2842 (1998)]. We study the parametric oscillator case and find that an entangled Schrödinger-cat-type state of two cavities, whose mirrors are placed along the output beams of the nonlinear crystals, can be realized under suitable conditions.