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تسجيل مستخدم جديدTwo methods for measuring Bell nonlocality via local unitary invariants of two-qubit systems in Hong-Ou-Mandel interferometers
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We describe a direct method to experimentally determine local two-qubit invariants by performing interferometric measurements on multiple copies of a given two-qubit state. We use this framework to analyze two different kinds of two-qubit invariants of Makhlin and Jing et. al. These invariants allow to fully reconstruct any two-qubit state up to local unitaries. We demonstrate that measuring 3 invariants is sufficient to find, e.g., the optimal Bell inequality violation. These invariants can be measured with local or nonlocal measurements. We show that the nonlocal strategy that follows from Makhlins invariants is more resource-efficient than local strategy following from the invariants of Jing et al. To measure all of the Makhlins invariants directly one needs to use both two-qubit singlet and three-qubit W-state projections on multiple copies of the two-qubit state. This problem is equivalent to a cordinate system handness measurement. We demonstrate that these 3-qubit measurements can be performed by utilizing Hong-Ou-Mandel interference which gives significant speedup in comparison to the classical handness measurement. Finally, we point to potential application of our results in quantum secret sharing.
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We describe a direct method for experimental determination of the negativity of an arbitrary two-qubit state with 11 measurements performed on multiple copies of the two-qubit system. Our method is based on the experimentally accessible sequences of
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