Electrons are always detected as particles, but can also show wave properties. This apparently incompatible nature of electrons that quantum mechanics predicts can now be experimentally demonstrated. In addition, the wave properties of electrons can be utilized to directly observe quantum phenomena which have begun to appear at many places in nanoscopic regions. Examples include the observation of quantized vortices in superconductors by using bright electron beams we developed.
Electrons are always detected as particles, but can also show wave properties. This apparently incompatible nature of electrons that quantum mechanics predicts can now be experimentally demonstrated. In addition, the wave properties of electrons can be utilized to directly observe quantum phenomena which have begun to appear at many places in nanoscopic regions. Examples include the observation of quantized vortices in superconductors by using bright electron beams we developed.
Fundamental aspects of quantum mechanics, which were discussed only theoretically as "thought experiments" in the 1920s and 1930s, have begun to frequently show up in nanoscopic regions owing to recent rapid progress in advanced technologies. Quantum phenomena were once regarded as the ultimate factors limiting further miniaturization trends of microstructured electronic devices, but now they have begun to be actively used as the principles for new devices such as quantum computers. To directly observe what had been unobservable quantum phenomena, we have tried to develop bright and monochromatic electron beams for the last 35 years. Every time the brightness of an electron beam improved, fundamental experiments in quantum mechanics became possible, and quantum phenomena became observable by using the wave nature of electrons.
Quantum phenomena have become directly observable with the development of advanced techniques such as coherent field-emission electron beams, sensitive detectors, and microlithography. Examples are the single-electron build-up of an interference pattern, which contains, as R. Feynman describes in his textbook, the heart of quantum mechanics, and the Aharonov–Bohm (AB) effect, which indicates the physical significance of gauge fields. Using the AB effect, i.e., the fundamental principle behind the interaction of an electron wave with electromagnetic fields, new ways to directly observe previously unobservable microscopic quantum objects and phenomena were developed by detecting the phase of electrons.
Abstract The behavior of electrons provides several concrete examples of quantum phenomena. We consider electron spin properties, how electrons move, quantum randomness and the relationships between observables, quantum limits on empirical prediction, superpositions, interference effects, nonlocality, and the role of observation in generating quantum phenomena. Each illustrates the counterintuitive nature of quantum phenomena and provides a sense of the sort of phenomena that any satisfactory formulation of quantum mechanics must predict and explain.
Abstract Recent researches in experimental and theoretical Physics strongly indicate that both matter and radiation possess a dual aspect exhibiting, on the one hand, the properties of undulatory phenomena extensible throughout the space-time continuum, and on the other, those of “parcel” or particle phenomena concentrated in small regions, the so-called “world lines” of particles. The wave mechanics of de Broglie and Schrödinger is an attempt to bridge the gulf, so to speak, between matter and radiation; and the question naturally arises as to whether these two apparently distinct entities may not represent the same, or at least similar, world conditions. Let (Ox, Oy,Oz) be a rectangular system of axes at rest relative to a material observer, and consider the motion of an electron relative to the observer. First, let the electron be conceived as a particle, as a region of the observer’s space bounded by a movable surface. It will be necessary for the following analysis to assign to this surface a definite form, and I shall choose the form of a Heaviside ellipsoid associated with the Lorentz electron, since this is the only form that is known to satisfy the geometrical conditions of the space-time continuum.
The years of the third decade of the present century were heady times. Old social orders were being swept away, monarchies becoming republics and the United States of America was emerging as a world power. In physics too, revolutions were taking place, none more potent than that which resulted in the emergence of quantum mechanics as a model for the behaviour of sub-atomic particles. It was Newton who first suggested that light was particulate but during the nineteenth century this view had fallen into neglect. Indeed a number of experiments, for example the classic Young's slits experiment, demonstrated quite conclusively that light was a wave motion. How else could interference fringes occur? However, the experiments on the photoelectric effect demonstrated just as conclusively that light energy was carried in packets, or quanta, and that a continuous wave description was not applicable. This ‘wave or particle’ dilemma was not unique to the behaviour of light. J. J. Thompson showed that cathode rays were charged, had a well defined mass and had all the properties expected of a beam of particles. Nevertheless, Davisson and Germer showed that diffraction of electrons could take place, an effect made visually much more dramatic by G. P. Thompson's transmission electron diffraction patterns. Nowadays, electron diffraction is used as a routine analytical tool in all advanced metallurgical and materials science laboratories (Fig. 2.1). Clearly new axioms were required.