Physica B+C最新文献

For cellular automaton machines getting increasingly smaller in size, a regime will be entered where effects due to matter waves may become dominant. Studying the evolution of one-dimensional and locally interacting cellular automata governed by generalized quantum mechanical rules, we discuss irreversibility as it appears in the evolution of structures in quantum cellular automata.

The Schrödinger paradox points out that quantum mechanics predicts a linear superposition of states even for macroscopic objects prior to measurement. However, at the macroscopic level of ordinary objects it has not been possible to maintain the phase correlations needed to demonstrate or disprove the reality of such a superposition of states as opposed to the mixture of states. Without such a quantum “signature”, this paradoxical prediction of quantum theory would seem to have no testable consequences. State vector collapse in that case becomes indistinguishable from a stochastic ensemble description.

The experiment described here provides a means for testing Schrödingers' paradox. A Michelson interferometer is used to test for the presence of state superposition of a pair of shutters that are placed along the two optical arms of the interferometer and driven by a beta decay source so that either the first shutter is open and the second closed or vice versa. The shutters take on the role of the cat in the Schrödinger paradox.

The experiment that we discuss here has been carried out at SRI International. Under the conditions of the experiment, the results remove the possibility of the existence of macroscopic superposition prior to observation.

We report the results of neutron interferometric experiments, extending the range and precision of the COW gravitationally-induced quantum interference experiment of Staudenmann and co-workers. These experiments provide a test of the principle of equivalence in the quantum limit. High precision data (1 part in 1000) is presented. The frequency of the quantum interference oscillations, and the loss of contrast observed as a function of increasing gravitational potential energy difference are compared with the recent interferometer dynamical diffraction calculations of Bonse and Wroblewski and of Horne. Theory and experiment are found to differ by 0.8%.

The operation of a two-thick-crystal LL neutron interferometer is strongly dependent on the size of the entrance slit as compared to the “Pendellösung length”. In the case of a narrow slit, the ray-optics formalism breaks down and the intensity profile around the center of the Borrmann fan of the second crystal, where focussing occurs, has to be calculated from the Green function which is the wave function in the observation plane for a point-source of the entrance slit, the different points of this slit being considered as incoherent. This Green function, which takes into account the presence of a test object on the beam path between the crystals, is normally a complicated integral expression. This leads to lengthy numerical calculations. It is shown that for a phase gradient φ between the crsytals, the Green function can be expressed by an expansion in terms of the Bessel functions J_2n(&φ;).

Two different applications of matter wave interferometry are presented and discussed. The first is aimed at investigating the interference fringe shift generated by a macroscopic electric dipole. This experiment represents the electrostatic analogue of the Aharonov-Bohm effect involving time-dependent scalar potentials. The second concerns a practical application of the electron holography technique to the mapping of the total field associated with reverse biased p-n junctions.

To examine experimentally, whether there are differences between the two-beam Dirac self-interferences of massless and massive particles, modifications of the electron biprism and the neutron double-slit interferometer are proposed as follows: (a) extension of the biprism techniques from electron to photon or heavier ions, and (b) macroscopic elongation in the two-beam interferometers, of the total separated path lengths (TSPL) which are different from the conventional path difference.

The idea, that the interference fringes for heavy masses should become more obscure as the TSPL are lengthened, seems to be conceivable for a natural model, which assumes a kind of spontaneous in-flight transition before the so-called observation starts since the arrival at the counter.

The relationships between the in-flight transition and Prigogine's microscopic irreversible scattering are discussed.

The Aharonov-Bohm effect (AB effect) involves fundamental problems in quantum mechanics such as the reality of vector potentials, the locality of physical effects, and the single-valuedness of the wave function in multiply connected spaces. Therefore various kinds of discussions have continuously been made for these 30 years. In this controversy, some people even negated the existence of the AB effect, attributing the experimental results previously performed to the Lorentz force effect due to the overlap between the electron and the magnetic field. In order to settle this situation, new experiments were carried out and the controversy entered a new phase.

The wave-like attributes of matter have been examined in numerous interference experiments exhibiting the first-order coherence of the particle field. Intensity fluctuation and correlation experiments, such as pioneered in light optics by Hanbury Brown and Twiss, manifest second-order coherence, a measure of particle clustering behaviour. Experiments of this nature have not, as yet, been performed on massive particle beams. The cross-correlation of output beams in a Mach-Zehnder fermion interferometer is sensitive to the coherence properties of multiparticle input states and to the quantum mechanical interaction of such states with potential fields such as electromagnetic potentials or gravity. Examples of both one- and two-port input beams are considered.

We have measured the phase shift of a neutron de Broglie wave induced by the motion of Sm-149 through which the neutron is propagating. This experiment differs from a number of ‘neutron Fizeau’ experiments carried out in recent years. The observed phase shift is caused by the motion of the matter itself, and not by the motion of its boundaries, as was the case with the earlier experiments. In this regard our experiment is a true neutron analog of the famous Fizeau experiment of 1859, where phase shift of the light wave interference pattern was induced by the motion of matter.