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KTH/Nordita/SU seminar in Theoretical Physics

Macroscopic quantum contextuality

by Prof. Adan Cabello (University of Sevilla)

FA31 ()


Quantum mechanics is supposedly universal. That is, applicable to any physical system on which experiments can be made. However, the kind of phenomena that have made quantum mechanics striking, like the nonexistence of definite noncontextual values and the need of superpositions to describe the state of a system is supposedly relevant only for "subatomic" or "microscopic" systems. The prevalent idea is that, the more complex the system is, the greater the effect of noise and decoherence, thus quantum phenomena become unobservable beyond relatively simple systems. Here we show that there is an inequality for the correlations between three sequential measurements, which must be satisfied by any description with definite noncontextual values, but is violated by quantum mechanics for any state of any physical system of n>1 qubits. Its remarkable feature is that the violation predicted by quantum mechanics is such that the maximum tolerated error in the measurements allowing a violation of the inequality grows with n. This opens the possibility of observing quantum contextuality in complex systems.