AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |
Back to Blog
Independently in 1984, Michael Berry at Warwick University, Coventry, UK, showed that quantum systems could acquire what is known as a geometric phase under certain conditions. Tonomura received numerous prizes for this work.įigure 1. In other words, electrons passing through regions free of any electromagnetic field, nevertheless interacted with the vector potentials in the regions. 1(a), interference fringes are displaced with just half-fringe spacing inside and outside of the doughnut, proving the existence of the AB effect. With the magnet maintained at a temperature of 5 K, they measured the phase difference from the interference fringes between one electron beam passing though the hole in the doughnut and the other passing on the outside of the doughnut. 1(a) and (b)), and covered it with a niobium superconductor to completely confine the magnetic field within the doughnut. To settle this dispute, Tonomura and his colleagues made a doughnut-shaped ferromagnet six micrometers in diameter (Fig. If so, the experiment did not prove the existence of the AB effect. there were leakage magnetic fields in space, that could have created the phase differential. As the electron beams contacted the magnet, i.e. Soon after publishing the results, an objection was raised to this experiment. They clearly showed that there is a phase difference between the two electrons beams passing through regions of space that have no magnetic field, and that the extent of the phase difference precisely matches the predicted value. In 1982, using a holography electron microscope Tonomura and his colleagues measured the phase difference in the form of interference fringes produced by two beams of electrons, one passing through the inside and the other passing through the outside of a doughnut-shaped magnet. This enabled him to pick out perfect magnets that do not leak magnetic fields to the outside. This was the basis of a technique known as electron holography, an interference electron microscopy that could be used to show up the contour map of the electron phase. In the 1970s, Tonomura succeeded in making a highly coherent electron microscope - with coherence more than two orders of magnitude higher than that of a conventional electron microscope. So, electron beams split into components that pass through the middle and the outside would be expected to have a different phase. In such a magnet, the magnetic field is trapped inside, and no magnetic field exists either in the hole in through the middle or in the space outside the torus. One of the more remarkable experiments to demonstrate the Aharonov-Bohm (AB) effect was carried out by Akira Tonomura of Hitachi Laboratory in Japan, using microscopic toroidal (doughnut shaped) magnets. The effect was soon observed in experiments. Aharonov and Bohm predicted that, according to quantum theory - described by Schrödinger's wave function - the two beams, being wave-like, would acquire different phases due to their interaction with the vector potential, even though the field itself was zero, and that the difference between these phases could be detected via interference. Although the magnetic field is zero outside the solenoid, the vector potential associated with the field is not zero. The beam is split into two so that one passes to the left and the other to the right of the solenoid. In 1959, quantum physicists Yakir Aharonov and the late David Bohm at Birbeck College, London University, proposed a thought-experiment in which an electron beam is directed towards a long thin magnetic field trapped inside a tightly-wound coil of electric wire, a solenoid. In classical electromagnetic theory, the vector and scalar potentials in Maxwell's equations of the electromagnetic field are purely mathematical entities without physical significance, but not so in quantum mechanics. Mae-Wan Ho investigates the link between quantum phases and quantum coherence, and comes up with the surprising implication that the universe itself may be quantum coherent Quantum phases
0 Comments
Read More
Leave a Reply. |