Physica B+C最新文献

It is shown that the quantum potential approach to quantum mechanics, originated by de Broglie and Bohm, can account for the essential features of spatial interference and spin superposition, observed with neutron interferometers, in terms of well-defined individual particle motions.

A novel resonant enhancement of the spin-orbit scattering of thermal neutrons in a perfect crystal is predicted. The effect occurs when the Larmor precession distance for the neutron in an externally applied magnetic field coincides with the pendellösung distance in the crystal. The potential is described, the wave functions are derived, and an experiment is proposed.

Quantitative measures are introduced for the indistinguishability U of two quantum states in a given measurement, and the amount of interference I observable in this measurement. It is shown that these notions obey an inequality $\text{U ≧ I}$, which can be seen as an exact formulation of Bohr's claim that one cannot distinguish between two possible paths of a particle while maintaining an interference phenomenon. This formulation is applied to a neutron interferometer experiment of Badurek et al. It is shown that the formulation is stronger than an argument based on an uncertainty relation for phase and photon number as considered by these authors.

Physical implications of the neutron interference experiments are discussed from the viewpoint of the many-Hilbert-spaces theory of quantum measurements, which provides a definite criterion for measuring apparatus to give wave packet reduction. We stress that the neutron interference experiments serve for a counter test of quantum measurement theories.

Experiments are reported, where one of the beams inside the neutron interferometer was attenuated in three different ways: by partially absorbing gold or indium foils, by a slow beam chopper and by a fine cadmium lattice. When the attenuation was the same the different methods still had a different effect on the amplitude of the interference pattern. This counter intuitive result can be formally explained in a quantum mechanical analysis which nicely illuminates how the history of a neutron affects its wave function.

Very slow neutrons with matter wave frequencies ⩽10¹¹ Hz offer the possibility to observe “diffraction in time”, the spreading in frequency (and velocity) die to the interaction with time varying potentials. These effects can be regarded as a test of the time dependent Schrödinger equation and of the uncertainty principle $\text{ΔE · Δt =}\text{h}\text{̵}$.

As a first step we will try to observe “diffraction in time” from a fast chopper with opening times (and repetition times) of about 2(6) × 10⁻⁸s. The spreading in travel time will be observed by a new high resolution time of flight spectrometer for 30 Å neutrons, which is currently under construction. With the nominal relative energy resolution of about 8 × 10⁻⁴ we expect interferences in time from successive openings of the chopper. This can be regarded as the double slit experiment in time. In a later version it seems possible to achieve chopper frequencies close to matter wave frequencies of 200 Å neutrons.

A spectrometer for carrying out perfect crystal diffractometry and neutron interferometry is proposed to be set up at the new 100 MW research reactor Dhruva, as part of a programme to expand and upgrade neutron beam based research activities at the Bhabha Atomic Research Centre (BARC). At present a facility has been set up at the CIRUS reactor where interference oscillations have been recorded using a symmetric LLL silicon interferometer. The setup at CIRUS will serve as a test bed for development of interferometry in BARC.

40 years after Gabor's proposal of electron holography, electron image plane off-axis holography using the Möllenstedt type electron biprism is able to investigate the electron object wave by its amplitude and phase at atomic dimensions.

Double crystal diffractometry is used for investigations in the field of neutron optics of perfect and nearly perfect crystals as well as for small-angle neutron scattering. It is demonstrated on the Si (220) reflection, that the structure factor for perfect crystal reflections can be determined with an accuracy of 0.1% by the simple inclination method. In implanted crystal slices the deformation of the crystal lattice near the implanted layer is investigated. Moreover, the change of this deformation field after light irradiation annealing is proved. Small-angle neutron scattering measurements in the momentum transfer range from 1 × 10⁻⁴ nm⁻¹ to 0.5 nm⁻¹ are possible by using a double crystal diffractometer equipped with perfect or elastically bent crystals. Applying an analyser crystal in fully asymmetric geometry the angular dependence of the SANS intensity is transformed in a positional one, which enables us to employ a position-sensitive detector.