G. Badurek

Verification of coherent spinor rotation of fermions

Abstract The perfect crystal neutron interferometer was used to test the spinor rotation of spin- 1 2 -systems. Coherently splitted unpolarized slow neutrons exposed partially to a variable magnetic field show interference oscillations which are consistent with the predicted 4π-value.

Violation of a Bell-like inequality in single-neutron interferometry.

Non-local correlations between spatially separated systems have been extensively discussed in the context of the Einstein, Podolsky and Rosen (EPR) paradox and Bells inequalities. Many proposals and experiments designed to test hidden variable theories and the violation of Bells inequalities have been reported; usually, these involve correlated photons, although recently an experiment was performed with 9Be+ ions. Nevertheless, it is of considerable interest to show that such correlations (arising from quantum mechanical entanglement) are not simply a peculiarity of photons. Here we measure correlations between two degrees of freedom (comprising spatial and spin components) of single neutrons; this removes the need for a source of entangled neutron pairs, which would present a considerable technical challenge. A Bell-like inequality is introduced to clarify the correlations that can arise between observables of otherwise independent degrees of freedom. We demonstrate the violation of this Bell-like inequality: our measured value is 2.051 ± 0.019, clearly above the value of 2 predicted by classical hidden variable theories.

Experimental demonstration of a universally valid error–disturbance uncertainty relation in spin measurements

Here, we reply to the comment by Y. Kurihara. We show that the argument by the author is on an improper basis and thus disagree with his opinion.

Quantum Zeno effect with neutron spin

Abstract The meaning and occurrence of quantum Zeno effects is discussed by making use of a simple experimental proposal involving neutron spins. The role of quantum measurements and “collapse of the wave function” is investigated and clarified. It is argued that in some cases a quantum Zeno phenomenon is a natural consequence of the evolution of a quantum system. A detailed experimental scheme is given for an experimental verification.

Violation of Heisenberg's error-disturbance uncertainty relation in neutron spin measurements

In its original formulation, Heisenbergs uncertainty principle dealt with the relationship between the error of a quantum measurement and the thereby induced disturbance on the measured object. Meanwhile, Heisenbergs heuristic arguments have turned out to be correct only for special cases. An alternative universally valid relation was derived by Ozawa in 2003. Here, we demonstrate that Ozawas predictions hold for projective neutron-spin measurements. The experimental inaccessibility of error and disturbance claimed elsewhere has been overcome using a tomographic method. By a systematic variation of experimental parameters in the entire configuration space, the physical behavior of error and disturbance for projective spin-

Explicit experimental verification of quantum spin-state superposition☆

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Basic features of the upgraded S18 neutron interferometer set-up at ILL

measurements is illustrated comprehensively. The violation of Heisenbergs original relation, as well as the validity of Ozawas relation become manifest. In addition, our results conclude that the widespread assumption of a reciprocal relation between error and disturbance is not valid in general.

Polarized neutron interferometry: A survey

Abstract An interferometric experiment with polarized neutrons is described that demonstrates the basic principles of coherent spin-state superposition in an explicit way.

Measurement of coherent neutron scattering lengths of gases

Abstract The perfect crystal interferometer instrument S18 at the Institute Laue-Langevin (ILL) in Grenoble has been upgraded to allow more advanced neutron optics experiments for fundamental, nuclear and condensed matter physics. The new supermirror guide together with the multipurpose monochromator provides considerably higher intensities in a wide wavelength region. The optimal use of neutrons is obtained by a nondispersive arrangement of the monochromator and the interferometer crystals. This also allows to obtain completely polarised beams using permanent magnetic prism deflection. An additional third analyzer axis permits novel postselection experiments concerning momentum distribution and polarisation analysis of the interfering beams. Several types of large perfect crystal interferometers are available for different applications. The system can be configured as an advanced high-resolution Bonse–Hart small angle scattering camera. The results of various test measurements concerning intensities, interference contrast, long-term stability, the accessible wavelength range and the basic features as a SANS camera will be presented. Various proposals for experiments will be discussed as well.

Reconstruction of the spin state

Abstract A brief summarizing review is given of all those neutron interferometric experiments performed hitherto which explicitly use the spin- 1 2 particle properties of the neutron. It covers topics as the verification of the 4π-periodicity of spinors, the cooperative action of nuclear phase shift and spin-rotation on the neutron wave function, the demonstration of the quantum mechanical principles of fermion spin-state superposition and the more recent double resonance experiments where the two interfering beams propagate through spatially separated oscillatory magnetic fields. Finally a proposal will be presented also for a so-called “late-choice” experiment with polarized neutrons.