Simulation Separability — An Intrinsic Notion of Separability

Sammanfattning

Entanglement is not an intrinsic property of a quantum state: it depends on how the total system is factorized into subsystems via a tensor product structure. Just as a coherent quantum state can be made to appear classical by representing it in its eigenbasis, an entangled state can always be made to appear separable in a suitably chosen factorization. However, the same is not true for a set of states. It is not always possible to make a set of states simultaneously separable in a common factorization. Following recent work that defined a basis-independent notion of classicality for sets of states, we propose an extension of this idea to sets of bipartite states. This leads us to a factorization-independent notion of separability we call simulation separability. This notion is weaker than previously studied forms of separability for sets of states. It can be physically understood via an operational interpretation based on unitary gates and state-preparation devices that emit separable states. By showing that the set of all simulation-separable sets is convex, we are able to derive necessary and sufficient conditions for simulation separability. We also propose an experimentally implementable method for detecting sets that are not simulation separable. Finally, finite sets of two-qubit states are investigated numerically with respect to simulation separability.