Experimental Demonstration that No Tripartite-Nonlocal Causal Theory Explains Nature's Correlations

Area of Science:

• Quantum Information Science
• Foundations of Physics
• Quantum Correlations

Background:

• Quantum theory predicts genuinely tripartite-entangled states, irreducible from bipartite entanglement.
• These states are fundamental signatures distinguishing quantum mechanics from classical theories.
• Previous work proved the necessity of tripartite resources for quantum predictions.

Purpose of the Study:

• To experimentally verify the existence and achievability of genuinely tripartite quantum correlations.
• To falsify causal theories limited to bipartite nonclassical resources.
• To generalize findings to higher-order entangled states like |GHZ_{4}⟩.

Main Methods:

• Derivation of a new device-independent witness for tripartite correlations.
• Generation of high-fidelity photonic |GHZ_{3}⟩ states (fidelity 0.9741±0.002).
• Experimental violation of the witness under locality and fair sampling assumptions.

Main Results:

• Clear experimental violation of the device-independent witness by over 26.3 standard deviations.
• Demonstration that observed correlations cannot be explained by bipartite nonclassical common causes.
• Successful generalization to |GHZ_{4}⟩ states, showing limitations of tripartite causal theories.

Conclusions:

• Genuinely tripartite entanglement is experimentally realizable and essential for quantum correlations.
• Quantum mechanics necessitates resources beyond classical or bipartite-limited causal theories.
• The findings confirm the fundamental role of multipartite entanglement in quantum information.