# Geometric representation of two-qubit entanglement witnesses

@article{Milne2014GeometricRO, title={Geometric representation of two-qubit entanglement witnesses}, author={Antony Milne and David Jennings and Terry Rudolph}, journal={Physical Review A}, year={2014}, volume={92} }

Any two-qubit state can be represented geometrically by a steering ellipsoid inside the Blochsphere. We extend this approach to represent any block positive two-qubit operator B. We derive a classification scheme based on the positivity of detBand de t B T B; this shows that any ellipsoid inside the Bloch sphere must represent either a two-qubit state or a two-qubit entanglement witness. We focus on such witnesses and their corresponding ellipsoids, finding that properties such as witness…

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