Falsification of Leggett's model using neutron matter waves

Abstract

According to Bell's theorem, no theory based on the joint assumption of realism and locality can reproduce certain predictions of quantum mechanics. Another class of realistic models, proposed by Leggett, that demands realism but abandons reliance on locality, is predicted to be in conflict with quantum mechanics. In this paper, we report on an experimental test of a contextual realistic model analogous to the model of Leggett performed with matter waves, more precisely with neutrons. Correlation measurements of the spin-energy entangled single-particle system show violation of a Leggett-type inequality by more than 7.6 standard deviations. Our experimental data falsify the contextual realistic model and are fully in favor of quantum mechanics.

Investigations of fundamental phenomena in quantum mechanics with neutrons

“…In this paper, recent experiments with the neutron interferometer and the polarimeter are presented. The interferometry studies properties of quantum system triply-entangled between degrees of freedom [8] and the polarimetry investigates a contextual modelá la Leggett [9]. In addition, successive measurements of neutron's spin [10,11] exhibits the violation of the naive error-disturbance relation by Heisenberg and confirms the validity of a new universally valid error-disturbance relation by Ozawa [12,13].…”

“…Here, we describe a falsification of a contextual realistic modelá la Leggett using neutrons [9]. In 2003, Leggett proposed a non-local realistic model [40], and an extension of Leggett's model appeared later [41].…”

Tripartite entanglement in single-neutron interferometer experiments

“…Entanglement purely between degrees of freedom in a single quantum system is extensively studied by using neutron optical techniques in particular neutron interferometry [1]: starting with a demonstration of the violation of a Bell-like inequality [2], the implementation of a triply entangled Greenberger-Zeilinger-Horne (GHZ)-like state is reported [3]. Quite recently, a test of an alternative model of quantum mechanics á la Leggett [4] as well as high-efficiency manipulations of a tripartite-entangled system [5] are reported by using another strategy, namely, neutron polarimetry. It is worth noting here that these neutron optical techniques exploit matter-waves and are very suitable to study properties of multipartite entangled systems of matter-waves, since the efficiency of manipulating degrees of freedom in a single neutron is rather high.…”

High-efficiency manipulations of triply entangled states in neutron polarimetry

“…Neutron polarimetry has been used to demonstrate fundamental quantum-mechanical properties, such as the noncommutation of the Pauli spin operator [30] and a number of geometric phase measurements [31][32][33]. In recent experiments, a test of Leggett's model, which is based on nonlocality and realism [34], as well as demonstration of a universally valid uncertainty relation [35] have been performed successfully.…”