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物性研究

中性子干渉をめぐる最近の話題と将来問題 : 吸収物干渉実験を中心に(基研長期研究計画「進化の力学への場の理論的アプローチ」報告,研究会報告)

美喜雄 並木, S. Pascazio

Published Aug 20, 1990• 0 citations
OpenAlex

Abstract

We analyze recent absorber neutron-interference experiments from the measurement-theoretical point of view, and show that the fluctuation effect inside absorbers can reduce observed values of the visibility to those lower than as expected by elementary quantum mechanics. We also briefly discuss implications of interference experiments by means of short neutron pulses, and future problems on possible experiments by means of cold neutron beams.

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Ukrainian Journal of Physics•Apr 30, 2012•0 citations
We analyze recent absorber neutron-interference experiments from the measurement-theoretical point of view, and show that the fluctuation effect inside absorbers can reduce observed values of the visibility to those lower than as expected by elementary quantum mechanics. We also briefly discuss implications of interference experiments by means of short neutron pulses, and future problems on possible experiments by means of cold neutron beams.
Experiments with absorbing foils, beam choppers, or an absorbing lattice in one path of a neutron interferometer to expose the difference between stochastic and deterministic absorption in quantum mechanics are reported. The different amplitudes of the interference patterns in stochastic and deterministic absorption when the absorption probability is the same were observed in agreement with prediction. Also the possibility of a gradual transition from deterministic to stochastic absorption was experimentally investigated.
We analyze some interesting and peculiar phenomena that appear both in the well-known classical domain and in the quantum domain, related to the behavior of the visibility in interference experiments. One can show that, according to its usual definition, the visibility is not a monotonic function of appropriate quantities, such as the optical path difference. In the quantum domain, the visibility can be used to infer the quantum mechanical coherence properties of a quantum particle, like for example a neutron, interacting with a fluctuating environment. In some cases the wave function is more coherent even though it has interacted with a more disordered medium. We will refer to these results as anomalous, because they are against naive expectations.
Single-particle interference phenomena can be observed with neutrons, and the "entanglement of degrees of freedom", i.e. the contextuality, can be verified and used in further experiments. Entanglement of two photons or atoms is a complementary situation to the double-slit diffraction of a single photon, neutron, or atom. In this respect, neutrons are proper tools for testing quantum mechanics, because they are massive, they couple to electromagnetic fields due to their magnetic moment, and they are subject to all basic interactions, and they are sensitive to topological effects as well. The4π-symmetry of spinor wave functions, the spin-superposition law, and many topological phenomena can be made visible, which shows interesting intrinsic features of quantum physics. Related experiments will be discussed. Deterministic and stochastic partial absorption experiments can be described by Bell-type inequalities. Recent neutron interferometry experiments based on post-selection methods have renewed the discussion about quantum non-locality and the quantum measuring process. It has been shown that interference phenomena can be revived even when the overall interference pattern has lost its contrast. This indicates a persisting coupling in the phase space even in cases of spatially separated Schrödinger cat-like situations. These states are extremely fragile and sensitive against any kind of fluctuations and other de-coherence processes. More complete quantum experiments also show that a complete retrieval of quantum states behind an interaction volume becomes impossible in principle.