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Heinz von Foerster 100
Organizing Institutions:
Heinz von Foerster Gesellschaft / Wien
ASC – American Society for Cybernetics
WISDOM – Wiener Institut für
  sozialwissenschaftliche Dokumentation und Methodik

Institut für Zeitgeschichte | Universität Wien
AINS – Austrian Institute for Nonlinear Studies
Helmut Rauch

Particle or/and wave features in neutron interferometry

Vienna University of Technology
Vienna, Austria

Matter wave interferometry provides new information about basic features how particles behave in a quantum environment. Thermal neutrons with energies about 25 meV are a proper tool for such investigations since widely separated coherent beams can be produced and manipulated individually. Neutrons experience nuclear-, electromagnetic- and gravitational interactions and they appear as particle or as waves depending on the experimental situation. How a massive and non-separable particle can be transported over two widely separated interferometric beams remains an epistemological question. The perfect crystal silicon interferometer has been used where the perfect arrangement of the lattice planes provide the coherent beam splitting und superposition for such experiments. The verification of the 4p spinor symmetry of fermions, the spin-superposition law and various gravitational effects have been verified [1]. Topological (geometric) phases can be measured and used for advanced wave function reconstruction work. Weak and post-selection measurements provide new information about the physical situation in the far-field region of a wave packet and show how nonlocal interaction effects can be explained by far reaching parts of the partial waves constituting a wave packet. Coherence and decoherence are basic features of the wave picture of matter, which influence the dynamical and the topological quantum phases as well. Related experiments deal with the interaction of neutrons with noisy magnetic fields where phase fluctuations and photon freedom [2]. Just the geometric phase shows a surprisingly high robustness against any fluctuation or dissipation process [3]. This may have consequences on quantum communication and quantum information systems. In a further step Kochen-Specker phenomena have been investigated which shows stronger correlations of basic features in quantum and particle physics than in classical physics.

[1] H. Rauch and S.A. Werner, "Neutron Interferometry", Clarendon Press, Oxford 2000
[2] Y. Hasegawa, R. Loidl, G. Badurek, M. Baron, H. Rauch, Nature 425 (2003) 45
[3] S. Filipp, J. Klepp, Y. Hasegawa, C. Plonka-Spehr, U. Schmidt, P. Geltenbort, H. Rauch, Phys. Rev. Lett. 102 (2009) 030404