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Demonstration of Quantum Nonlocality in presence of Measurement Dependence

Abstract : Quantum nonlocality stands as a resource for Device Independent Quantum Information Processing (DIQIP), as, for instance, Device Independent Quantum Key Distribution. We investigate experimentally the assumption of limited Measurement Dependence, i.e., that the measurement settings used in Bell inequality tests or DIQIP are partially influenced by the source of entangled particle and/or by an adversary. Using a recently derived Bell-like inequality [Phys. Rev. Lett. 113 190402 ] and a 99% fidelity source of partially entangled polarization photonic qubits, we obtain a clear violation of the inequality, excluding a much larger range of measurement dependent local models than would be possible with an adapted Clauser, Horne, Shimony and Holt (CHSH) inequality. It is therefore shown that the Measurement Independence assumption can be widely relaxed while still demonstrating quantum nonlocality. Introduction– The violation of a Bell inequality demonstrates that the observed correlations cannot be explained by any theoretical model based only on local variables that propagate gradually and continuously through space. This seminal result by John S. Bell [1] is nowadays considered fundamental for our understanding of quantum physics. Indeed, today the best way to demonstrate that one masters some quantum degree of freedom of some physical system is to violate a Bell inequality using this degree of freedom. Additionally, quantum nonlocality, i.e., the violation of a Bell inequality, is the resource physicists and computers scientists exploit in Device Independent Quantum Information Processing (DIQIP), like Device Independent Quantum Key Distribution [2, 3] and Device Independent Quantum Random Number Generators [4]. This dual fundamental-&-applied importance of quantum nonlocality has triggered an interesting scientific race to close both the locality and the detection loopholes simultaneously in one single experiment [5–9]. However, there is another sort of assumption in the derivation of Bell inequalities, that of Measurement Independence (also known as " Freedom of Choice " , " Free Randomness " , or sometimes loosely denoted by " Free Will "). This assumption states that the hypothetical local variable, traditionally referred to as λ, does not influence the local choices of measurement settings performed by the two parties Alice and Bob. Formally, denoting by x and y the measurement settings of Alice and Bob, respectively , this assumption reads [10, 11]: P (xy|λ) = P (xy) ∀x, y, λ. (1)
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Submitted on : Monday, June 8, 2015 - 2:49:54 PM
Last modification on : Tuesday, May 26, 2020 - 6:50:51 PM
Long-term archiving on: : Tuesday, April 25, 2017 - 4:45:40 AM

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Djeylan Aktas, Sébastien Tanzilli, Anthony Martin, Gilles Pütz, Rob Thew, et al.. Demonstration of Quantum Nonlocality in presence of Measurement Dependence. Physical Review Letters, American Physical Society, 2015, 114, pp.220404. ⟨10.1103/PhysRevLett.114.220404⟩. ⟨hal-01161453⟩

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