Neutron polarimetry has been established as an ideal technique for the investigation of foundations of quantum mechanics with massive particles. This is demonstrated especially in experiments where high stability and efficiency for observation of quantum mechanical phenomena are required: such as the noncommutation of the Pauli spin operator, geometric phase measurements and evidence of entanglement of different degrees of freedom in single neutron systems.
In this project we propose three major research targets:
(i) Development of a weak measurement procedure by means of a non-ideal Stern-Gerlach apparatus in neutron polarimetry
(ii) Investigation of topological phases, more precisely phases induced by non-unitary evolutions and an extension of the Sagnac effect, i.e., the Sagnac-Mashhoon effect
(iii) Quantum state tomographic (density matrix reconstruction) of a maximally entangled Bell state and a reconstruction of the Wigner functions of Schrödinger cat states (Neutron wave-packet tomography)
Assuming the value of an observable depends on both a pre- and a post-selected state vector Aharobov and his co-workers developed a so called weak measurement scheme, yielding measurement values (weak values), which may lie far outside the usual range of the observable's eigenvalues. An experimental demonstration using neutrons is still lacking. The second topic of our project is devoted to topological phase. Here we are interested in non-unitarity evolutions, which are usually considered in “open quantum systems. A geometric phase arising from an evolution path depends only upon the path traced out by the system, but is different from the usual geometric phase from unitary evolutions. In addition a neutron polarimetric version of the Sagnac effect, which originally describes the influence of rotation on the phase of light passing through an interferometer, is considered using a slowly rotating static magnetic field. The last topic of the project is entanglement detection, where a quantum state tomography of a quantum system consisting of two qubits (spin and total energy of the neutron) requires measuring a full set of 16 operators. A high-frequency spin flipper system, where due to the exchange of energy with the radiation field (via photons) spin and energy of the neutron are manipulated, forms the basis for density matrix and reconstruction and tomographic reconstruction of the Wigner functions of Schrödinger cat states. Therefore development of a state of the art high-frequency spin-flipper system is inevitable.
In this project, experimental investigations will have priority and theoretical support will be provided from collaborations with groups in Austria and worldwide. The aim of the project is to contribute to the impressive progress of quantum optics/communication technology and to better understand fundamental concepts of quantum mechanics by using specific properties of the neutron.
