Resource-efficient measurement device independent entanglement witness

Abstract

Imperfections in experimental measurement schemes can lead to falsely identifying, or over estimating, entanglement in a quantum system. A recent solution to this is to define schemes that are robust to measurement imperfections - measurement device independent entanglement witness (MDI-EW). Here we introduce a novel approach for MDI-EW, which significantly reduces the experimental complexity and is applicable to a wide range of physical systems. The scheme requires no prior description of the state, is detection loop-hole free, robust to classical communication, and works for all entangled qubit states. We focus on photonic entanglement, experimentally generating and testing bipartite Werner states, varying the entanglement from the maximally entangled Bell state, past the bound for nonlocal states and down to the separable bound of 1/3. We witness entanglement down to an entangled state fraction close to 0.4. These results could be of particular interest for device independent quantum random number generation.