Neutron interferometric experiments have long been established as an almost ideal tool to investigate
fundamental phenomena in quantum mechanics: in particular, those experiments, where interference
effects of matter waves of massive particles are involved, have served as elegant demonstrations related
to the foundations of quantum mechanics. This technique enabled many text-book experiments of
quantum physics such as demonstrations of 4¿ spinor symmetry of 1/2-spin, spin superposition,
gravitationally induced phase and non-inertial motional effects. In addition, utilizing interference effect
between two spin eigenstates, an alternative method using neutron polarimeters has turned out to be
another useful tool for investigations of quantum mechanical two-level system. This apparatus is used for
phase measurements, like topological phase measurements, particularly in cases where high stability and
efficiency are called for.
In this project, following our recent successful investigations of foundations of quantum mechanics
with neutrons, we proceed with investigations of weak values, i.e., extended values attained in
quantum measurements from conventional measurement results obtained via strong interaction,
with neutron’s matter waves. Four major research targets are proposed:
(i) Implementation of extracting weak values of matter waves via weak measurements as well as other
strategies, i.e., without weak measurements and weak interactions
(ii) Studies of weak values as a complex number in the neutron experiments as well as those of whichpath
information in relation to arguments of wave-particle duality
(iii) Studies of paradoxical phenomena in quantum mechanics relevant to weak values
(iv) Studies of weak values in terms of information in quantum measurements and as results of
extended quantum measurements
In the previous project “Double, triple and quadruple entanglement of neutrons” (July 2009 ~), we
accomplished the experimental implementation of a multi-partite entangled state in neutron
interferometers and polarimeters. In addition, a neutron polarimetric experiment confirmed the violation
of the old error-disturbance uncertainty relation by Heisenberg and the validity a new universally valid
formation. On the basis of these achievements, we believe that investigations of weak values with
neutron’s matter waves are now feasible: appropriate development of some needed optical elements will
enable the proposed experiments. Moreover, we hope that these experiments will exhibit new aspects of
quantum measurements which are more abundant in available information than those in classical physics.
In all cases experimental investigation will have priority and theoretical support will be provided
from collaborations with other groups, in Austria, Japan, France, India and worldwide. The aim of the
project is to contribute also to the impressive progress of quantum optics and quantum
information/communication technology by the use of the specific properties of neutrons as an elementary
matter wave system.