Experimentally demonstrating reference-frame-independent violations of Bell inequalities
Matthew S. Palsson, Joel J. Wallman, Adam Bennet, Geoff J. Pryde · Physical Review A · 2012
We experimentally demonstrate, using qubits encoded in photon polarization, that two parties who share a single reference direction and use locally orthogonal measurements will always violate a Bell inequality, up to experimental deficiencies. This contrasts with the standard view of Bell inequalities, in which the parties need to completely align their measurements. Furthermore, we experimentally demonstrate that as the reference direction degrades the probability of the observers randomly choosing measurements that violate a Bell inequality decreases gradually and smoothly to $39.7%\ifmmode\pm\else\textpm\fi{}0.1%$ in the limiting case that the observers do not share a reference direction. This result promises simplified distribution of entanglement between separated parties, with applications in fundamental investigations of quantum physics and tasks such as quantum communication.