Physica B+C最新文献

A topological phase factor arising from the homotopy theory of path integrals in multiply connected spaces is equivalent to the non-integrable phase of the Dirac wave function of a charge particle in the presence of an inaccessible, time-independent magnetic flux. The Aharonov-Bohm interference is analysed with the topological phase.

Already in 1935, Schrödinger assembled all prerequisites for a proof of Bell-type inequalities, namely: (i) a suitable two-particle state; (ii) a sufficient number of observables which are correlated in that state; and (iii) a tentative interpretation of these correlations in the spirit of local hidden-variables theories. The inequalities derived here from these assumptions are violated in quantum mechanics, which shows once more that quantum correlations cannot be understood in terms of local hidden-variables theories. This was realized before Bell (1964), since all previous authors — including Schrödinger — focused their attention to perfect correlations and underestimated the importance of the imperfect ones.

Previous studies on the one-dimensional motion of neutral spin $\text{1}\text{2}$ particles with an anomalous magnetic moment in magnetic fields in nonrelativistic [1] and relativistic [2] cases are extended to two- and three-dimensional motions. Dirac equation with Pauli coupling is solved exactly.

We consider a variant of Young's double-slit experiment with polarized photons for which quantum theory predicts that different amounts of angular momentum will be absorbed at a certain location M according as we set up a revolving plate or a Nicol prism at M. This difference, which implies a retroactive effect because angular momentum is a conserved quantity, can in principle be established experimentally. The relevant experiment differs fundamentally from Wheeler's delayed-choice experiments.

Another experiment is also discussed in which retroactivity cannot be expected to manifest, though it is seemingly similar to the first one.

Finally, we consider an analogous experiment with spin particles, in which it can also be expected from quantum mechanics that a retroactive effect will appear. Here, too, experimental verification is in principle possible.

Aberration distortions of wavefronts in a very cold neutron interferometer using diffraction gratings are analyzed. Aberrations that considerably reduce the efficiency of a two-grating interferometer are shown to be fully compensable by adding a third diffraction grating, which also permits the interferometer to operate with a non-collimated and non-monochromatized illuminating beam thereby raising its efficiency. A fourth diffraction grating additionally permits compensation of effects of the terrestrial rotation that affect performance of a large interferometer in which the spatial separation of beams can be of the order of a few meters.

It is demonstrated to be practically possible to implement an interferometer for neutrons having a wavelength λ = 20 Å and to use it in experiments aimed at finding the electric charge of the neutron at the level of 10⁻²³ to 10⁻²² of the electronic charge.

In some polarized neutron beam experiments, such as Neutron Spin Echo spectroscopy, it is essential to follow exactly the minute changes of the neutron kinetic energy due to interaction with the magnetic fields, e.g. in a spin flip process. It is emphasized that in the Amperian current loop model of microscopic magnetism, shown to be valid by the experiments, the Zeeman energy term can be treated as a bona fide potential energy. This allows us to describe both the spin and the spatial motion of the neutron by using simple notions of wave propagation across potential steps. In this picture Larmor precessions are represented as interference between two Stern-Gerlach states ↑ and ↓. The approach proves to be sufficient for the interpretation of all known polarized neutron beam phenomena, including crystal interferometry. It also leads to the surprising prediction that, as a pure quantum effect, under special circumstances the Larmor precession frequency can be different from its classical value.

The importance of quantum phenomena in semiconductor components, in particular in Si MOSFETs and GaAlAs/ GaAs heterostructures, is outlined. A short theoretical description of quantization effects in surface potential wells and at high magnetic fields is given. Multiple quantum well structures and modulation-doped heterostructures, as well as their possible applications are described. The discovery of the quantum Hall effect (QHE) is shown to be a result of the development of high-quality components. The features and the importance of the QHE for basic physics are outlined. Recent experimental data are discussed showing that the theoretical description of QHE is still unsatisfactory. A possible analogy of QHE to some features of superconductivity based on the idea of a changed effective mass is considered.

This paper presents experiments concerning momentum transfer to atoms by a standing light wave in the absence of spontaneous decay. This momentum transfer, which occurs in discrete units of 2 ħ k along the k-vector of the standing light wave, can be viewed as absorption/stimulated emission of photon pairs from the counterpropagating traveling waves which make up the standing light wave. In a dual sense, this phenomenon can also be viewed as diffraction of an atomic de Broglie wave from the periodic intensity grating of the standing light wave. In addition, we address how the inherent Heisenberg uncertainty between the focussed waist of the standing light wave and the angular spread of the k-vectors of photons traveling through this waist affects momentum transfer to the atoms by the light. For large widths of the standing light wave, the reduction of the uncertainty in the direction of the photons results in resonances for the momentum transfer only for discrete values of atomic momentum along the k-vector of the standing light wave which satisfy the Bragg condition. We present experimental data which display the Pendellösung effect for Bragg scattering of atomic de Broglie waves from a standing light wave. Finally, we discuss the possibility of exploiting these phenomena to build an atomic interferometer, one that interferes atomic de Broglie waves.