Quantum Physics with Neutrons: From Spinor Symmetry to Kochen-Specker Phenomena

Yuji Hasegawa, Helmut Rauch

Neutrons are suitable tools for quantum experiments since they are massive, experience nuclear, electromagnetic and gravitational interaction and are easy to manipulate and to detect. Perfect crystal interferometry opened new possibilities to explore quantum phenomena on a new ground. The 4 π -symmetry of spinor wave functions, the spin-superposition law, topological quantum phases and various gravitational effects have been examined using this method. Experiments exploiting contextuality and Kochen–Specker phenomena exhibit intrinsic entanglement in single particle systems. This may have consequences for a deeper understanding of quantum physics and for applications in future quantum communication systems.

Apoorva G. Wagh, Veer Chand Rakhecha

Helmut Rauch, Dipankar Home, Guruprasad Kar +1 more

Yuji Hasegawa, Rudolf Loidl, G. Badurek +2 more

An experimental demonstration of quantum contextuality with neutrons is presented, which intended to exhibit a Kochen-Specker-like phenomenon. Since no perfect correlation is expected in practical experiments, inequalities are derived to distinguish quantitatively the obtained results from predictions by a noncontextual hidden variable theory. Experiments were accomplished with the use of a neutron interferometer combined with spinor manipulation devices. The results clearly violate the prediction of noncontextual theories.

Yuji Hasegawa, Daniel Erdősi, Dipankar Home +2 more

There are two powerful arguments against the possibility of extending quantum mechanics (QM) into a more fundamental theory yielding a deterministic description of nature. One is the experimental violation of Bell inequalities, which discards local hidden‐variable theories as a possible extension to QM. The other is the Kochen‐Specker (KS) theorem, which stresses the incompatibility of QM with a larger class of hidden‐variable theories, known as noncontextual hidden‐variable theories. We performed experiments with neutron interferometer, which exploits spin‐path entanglements in single neutrons. A Bell‐like state is generated to demonstrate a violation of the Bell‐like inequality and phenomena in accordance with KS theorem: both experiments study quantum contextuality and show clear evidence of the incompatibility of noncontextual hidden variable theories with QM. The value S = 2.202±0.007≰2 is obtained in the new measurement of the Bell‐like inequality, which shows a larger violation than the previous measurement. For the study of KS theorem, the obtained violation 2.291±0.008≰1 clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden variable theories.

Helmut Rauch