Device-Independent Certification of a Nonprojective Qubit Measurement

Gómez, Esteban S. and Gómez, Santiago and González, Pablo and Cañas, Gustavo and Barra, Johanna F. and Vértesi, Tamás (2016) Device-Independent Certification of a Nonprojective Qubit Measurement. PHYSICAL REVIEW LETTERS, 117 (26). ISSN 0031-9007

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Abstract

Quantum measurements on a two-level system can have more than two independent outcomes, and in this case, the measurement cannot be projective. Measurements of this general type are essential to an operational approach to quantum theory, but so far, the nonprojective character of a measurement could only be verified experimentally by already assuming a specific quantum model of parts of the experimental setup. Here, we overcome this restriction by using a device-independent approach. In an experiment on pairs of polarization-entangled photonic qubits we violate by more than 8 standard deviations a Bell-like correlation inequality which is valid for all sets of two-outcome measurements in any dimension. We combine this with a device-independent verification that the system is best described by two qubits, which therefore constitutes the first device-independent certification of a nonprojective quantum measurement.

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