Experimentally Violating Bell Inequalities Without Complete Reference Frames

TL;DR

This paper demonstrates experimentally that sharing a single reference direction and using orthogonal measurements suffices to violate Bell inequalities, simplifying entanglement distribution and advancing quantum communication.

Contribution

It shows Bell inequality violations without complete shared reference frames, contrasting with standard requirements, and quantifies how violations diminish as reference sharing degrades.

Findings

Bell violations occur with shared single reference direction

Violation probability decreases smoothly as reference sharing degrades

Maximum violation probability observed is approximately 39.7%

Abstract

We experimentally demonstrate, using qubits encoded in photon polarization, that if two parties share a single reference direction and use locally orthogonal measurements they 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 share a complete reference frame for their measurements. Furthermore, we experimentally demonstrate that as the reference direction degrades the probability of violating a Bell inequality decreases smoothly to (39.7 +/- 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.