Generation of quadripartite unlockable bound entanglement from cascaded four-wave mixing processes

We propose a scheme for generating a continuous-variable (CV) quadripartite unlockable bound entangled state from cascaded four-wave mixing processes. Different from the previous method involving a bipartite entangled state and two thermal states, our results show that the CV quadripartite unlockable bound entangled state can be generated via the internal reconfiguration of a four-mode entangled state. Both the nondistillability and superactivation of the generated CV quadripartite unlockable bound entangled state can be demonstrated. We believe that our scheme is experimentally accessible and will contribute to a deeper understanding of CV multipartite unlockable bound entanglement.