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Quantum states are successfully reconstructed using the maximum likelihood estimation on the subspace where the measured projectors reproduce the identity operator. Reconstruction corresponds to normalization of incompatible observations. The proposed approach handles the noisy data corresponding to realistic incomplete observation with finite resolution., RevTeX, 4 pages, 3 figures

The limit of infinitely many measurements is critically analyzed within the quantum mechanical framework, in connection with the quantum Zeno effect. It is shown that such a limit is unphysical and that quantum losses are unavoidable. A specific example involving neutron spin is considered.

The limit of infinitely frequent measurements (continuous observation), yielding the quantum Zeno paradox, is critically analyzed and shown to be unphysical. A specific example involving neutron spin is considered and some practical estimates are given.

We study the motion of the neutron spin in an oscillating magnetic field within the frame of the WKB approximation. We calculate the neutron wavefunction and the orbit of the polarization vector on the unit sphere for the case where the Larmor precession frequency is much higher than the oscillation frequency of the magnetic field. Furthermore, we also present some other analytic methods to solve the spin equation of motion in an oscillating field. Finally we show that the geometric phase shift due to the oscillating field component vanishes.

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.

We present a simplified and improved analysis of some recent experiments of neutron interferometry at low transmission probability. It is shown that both the density fluctuations of the elementary constituents of the absorber and the uncertainties in the sample thickness can be analyzed with the same formalism, and that they lead to a reduction of the visibility of the interference pattern. The effect is quantitatively estimated in the Gaussian case. In the context of quantum measurements, the process can be viewed as a partial dephasing characterized by the decoherence parameter. Possible experimental tests are proposed.

Recent technical progress of neutron detection is shown to allow the simultaneous observation of interference and individual energy losses in neutron interferometric double resonance experiments. This detection which is also predicted by the present mathematical formalism of quantum mechanics is shown to support Einstein's “Einweg” point of view in double slit experiments provided the proposed experiments satisfy the predictions of the said formalism.

Recent neutron interference experiments have shown that a loss of interference in ordinary space is accompanied with a marked modulation in momentum space. This indicates that coherent wave packets remain coupled even in the case of wide spatial separation which has consequences for any EPR situation and for the discussion of nonlocality in quantum physics.

A.G. Wagh and V.C. Rakhecha noticed in their comment correctly that the geometric phase does not vanish if a static field exists besides the oscillating field. Here we show that in case of a vanishing static field, the geometrical phase becomes zero or very small in case packet properties are included.

Using two perfect silicon crystal lamellae of high quality we could detect the refractive bending of neutron waves within an aluminium prism down to 10 −3 s of arc by observation of the oscillatory fine structure of the rocking curve.

The spin-dependent retardation and acceleration of neutrons entering a magnetic field has been measured by means of the high resolution backscattering technique. Its relation to a neutron magnetic resonance system is discussed.

The effects of simultaneous phase shift and spin rotation on neutron waves were measured with the perfect crystal neutron interferometer. Using an unpolarized beam of slow neutrons characteristic “beat” effects of the interference pattern and a polarization of the neutrons behind the interferometer could be observed.

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.

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

Neutron absorption in one of the two beam paths of a neutron interferometer gives different interference pattern with static and with time-dependent absorption even when the time-averaged absorption is the same. This has been demonstrated by experiment.

The interference of two widely separated coherent neutron beams produced by dynamical diffraction in a perfect Si-crystal has been observed. Phase shifting material inserted in the beams results in a marked intensity modulation behind the interferometer. Neutron interferometry introduces several new feasible experiments in nuclear and solid state physics.

The calculation of time-independent spin correlation function for a Ising ferromagnet is performed with a Monte Carlo method in the case of a simple cubic lattice, S = ∞ and interactions only between nearest neighbours.

The interaction of polarized neutrons with superconductors in the Meissner, intermediate and mixed state is described. In increasing fields, only hysteretic type II superconductors show a distinct neutron depolarization. The almost ideal type II superconductors do not affect the polarization.

Using the neutron depolarization technique [1] more elaborate measurements were taken on several niobium samples showing a characteristic dependence of the flux line lattice distortions on hysteresis. The depolarization maximum seems to indicate the entrance of the sample into the overall critical state.