Remotely preparing Schrödinger cat states via non-Gaussian quantum steering in cascaded second-order spontaneous downconversion
Phys. Rev. A 113, 023712 – Published 17 February, 2026
DOI: https://doi.org/10.1103/skp5-nn4m
Abstract
Cascaded quadratic nonlinearities provide a practical alternative to the intrinsically weak direct third-order nonlinearities in conventional optical systems, enabling effective emulation of strong cubic nonlinear processes. In this work, we theoretically demonstrate the generation of Schrödinger cat states via non-Gaussian quantum steering in cascaded spontaneous parametric downconversion, considering both partially degenerate and fully nondegenerate configurations. We show that the pump amplitude can be tuned to control the degree of non-Gaussianity and entanglement in the resulting three-photon states. By extending Reid's Einstein-Podolsky-Rosen criterion to higher-order quadrature moments, we reveal non-Gaussian steering that remains undetectable using standard first-order quadrature measurements. This contrast confirms that the cascaded process generates a genuinely non-Gaussian state whose essential quantum correlations are encoded in higher-order statistical moments. Furthermore, we demonstrate how these non-Gaussian steerable correlations enable the remote heralding of high-fidelity, large-amplitude two- and four-component Schrödinger cat states through conditional homodyne detection. Our work establishes a direct connection between higher-order quantum correlations and controllable non-Gaussian state engineering, offering additional possibilities for fundamental tests of quantum physics and optical quantum technologies.
