Nonlocality activation in a photonic quantum network

Abstract

Bell nonlocality refers to correlations between two distant, entangled particles that challenge classical notions of local causality. Beyond its foundational significance, nonlocality is crucial for device-independent technologies like quantum key distribution and randomness generation. Nonlocality quickly deteriorates in the presence of noise, and restoring nonlocal correlations requires additional resources. These often come in the form of many instances of the input state and joint measurements, incurring a significant resource overhead. Here, we experimentally demonstrate that single copies of Bell-local states, incapable of violating any standard Bell inequality, can give rise to nonlocality after being embedded into a quantum network of multiple parties. We subject the initial entangled state to a quantum channel that broadcasts part of the state to two independent receivers and certify the nonlocality in the resulting network by violating a tailored Bell-like inequality. We obtain these results without making any assumptions about the prepared states, the quantum channel, or the validity of quantum theory. Our findings have fundamental implications for nonlocality and enable the practical use of nonlocal correlations in real-world applications, even in scenarios dominated by noise.

14 pages, 6 figures. Final version published in Nature Communications

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Cited by in corpus (7)

• Heralded generation of entanglement with photons
• Deterministic generation of multi-qubit entangled states among distant parties using indefinite causal order
• A robust approach for time-bin encoded photonic quantum information protocols
• Consequences of the single-pair measurement of the Bell parameter
• Experimental single-copy distillation of quantumness from higher-dimensional entanglement
• Nonlocal Josephson diode effect in minimal Kitaev chains
• Certifying the activation of Bell nonlocality with finite data