Abstract
The Clauser–Horne–Shimony–Holt (CHSH) inequality test is widely used as a mean of invalidating the local deterministic theories. Most attempts to experimentally test nonlocality have presumed unphysical idealizations that do not hold in real experiments, namely, noiseless measurements. We demonstrate an experimental violation of the CHSH inequality that is free of idealization and rules out local models with high confidence. We show that the CHSH inequality can always be violated for any nonzero noise parameter of the measurement. Intriguingly, less entanglement exhibits more nonlocality in the CHSH test with noisy measurements. Furthermore, we theoretically propose and experimentally demonstrate how the CHSH test with noisy measurements can be used to detect weak entanglement on two-qubit states. Our results offer a deeper insight into the relation between entanglement and nonlocality.
Highlights
Quantum systems exhibit a wide range of non-classical and counter-intuitive phenomena, such as quantum entanglement[1] and Bell nonlocality[2]
They consider a scenario in which one party has inefficient detectors and can only perform noisy measurements and show that the Clauser–Horne–Shimony–Holt (CHSH) inequality can always be violated for measurements with any nonzero detection efficiency
The violation of the CHSH inequality is even larger than that obtained by the state with more entanglement, which can be seen by comparing Fig. 4a, b
Summary
Quantum systems exhibit a wide range of non-classical and counter-intuitive phenomena, such as quantum entanglement[1] and Bell nonlocality[2]. Bell’s insight that nonlocal correlations between quantum systems cannot be explained classically can be verified experimentally and has numerous applications in modern quantum information[3,4,5,6,7,8]. Dilley and Chitambar[30] show how to devise the test that is free of the other idealization that measurements are noiseless, which is never satisfied precisely by any real experiment. They consider a scenario in which one party has inefficient detectors and can only perform noisy measurements and show that the Clauser–Horne–Shimony–Holt (CHSH) inequality can always be violated for measurements with any nonzero detection efficiency
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