  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.
