We implemented a triply entangled Greenberger-Horne-Zeilinger(GHZ)-like state
and coherently manipulated the spin, path, and energy degrees of freedom in a
single neutron system. The GHZ-like state was analyzed with an inequality
derived by Mermin: we determined the four expectation values and finally
obtained M = 2.558 +/- 0.004 > 2, which exhibits a clear violation of the
noncontextual assumption and confirms quantum contextuality.Comment: 4 pages, 2figure
We propose to test the electric neutrality of neutrons by a new technique using the spectroscopy of quantum states of ultracold neutrons in the gravity potential above a vertical mirror. The new technique is an application of Ramsey's method of separated oscillating fields to neutron's quantum states in the gravity potential of the Earth. In the presence of an electric field E z parallel or antiparallel to the direction of the acceleration of the Earth, g, the energy of the quantum states changes due to an additional electrostatic potential if a neutron carries a nonvanishing charge. In the long run our new method has the potential to improve the current limit of 10 À21 q e for the electric charge of the neutron by 2 orders of magnitude.
The Kochen–Specker theorem shows the
incompatibility of noncontextual hidden variable theories with quantum
mechanics. Quantum contextuality is a more general concept than quantum
non-locality which is quite well tested in experiments using Bell inequalities.
Within neutron interferometry we performed an experimental test of the
Kochen–Specker theorem with an inequality, which identifies quantum
contextuality, by using spin-path entanglement of single neutrons. Here
entanglement is achieved not between different particles, but between degrees of
freedom of a single neutron, i.e., between spin and path degree of freedom.
Appropriate combinations of the spin analysis and the position of the phase
shifter allow an experimental verification of the violation of an inequality
derived from the Kochen–Specker theorem. The observed violation
2.291±0.008≰1 clearly shows that quantum mechanical predictions cannot be
reproduced by noncontextual hidden variable theories.
The influence of the geometric phase on a Bell measurement, as proposed by Bertlmann et al. in [Phys. Rev. A 69, 032112 (2004)], and expressed by the Clauser-Horne-Shimony-Holt (CHSH) inequality, has been observed for a spin-path entangled neutron state in an interferometric setup. It is experimentally demonstrated that the effect of geometric phase can be balanced by a change in Bell angles. The geometric phase is acquired during a time dependent interaction with two radio-frequency (rf) fields. Two schemes, polar and azimuthal adjustment of the Bell angles, are realized and analyzed in detail. The former scheme, yields a sinusoidal oscillation of the correlation function S, dependent on the geometric phase, such that it varies in the range between 2 and 2 √ 2 and, therefore, always exceeds the boundary value 2 between quantum mechanic and noncontextual theories. The latter scheme results in a constant, maximal violation of the Bell-like-CHSH inequality, where S remains 2 √ 2 for all settings of the geometric phase.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.