Quantum Nonlocality Obtained from Local States by Entanglement Purification
Philip John Walther, Katharina Resch, Časlav Brukner, Aephraim M. Steinberg, Jian-Wei Pan, Anton Zeilinger · Physical Review Letters · 2005
We have applied an entanglement purification protocol to produce a single entangled pair of photons capable of violating a Clauser-Horne-Shimony-Holt Bell inequality from two pairs that individually could not. The initial poorly entangled photons were created by a controllable decoherence that introduced complex errors. All of the states were reconstructed using quantum state tomography which allowed for a quantitative description of the improvement of the state after purification.