NIST scientists observe dynamical tunneling. (News Briefs).The quantum mechanical phenomenon of tunneling, which allows a system to go from one state to another through a region that is classically forbidden, has been observed since the early days of quantum mechanics quantum mechanics: see quantum theory. quantum mechanics Branch of mathematical physics that deals with atomic and subatomic systems. It is concerned with phenomena that are so small-scale that they cannot be described in classical terms, and it is . Tunneling usually involves a particle going from one region to another through a barrier that classically the particle does not have sufficient energy to go over. Dynamical tunneling, predicted only since the early 1 980s, is a similar phenomenon where some other constant of the motion other than energy forbids classically the quantum-mechanically allowed motion. Imagine a wheel spinning either clockwise or counterclockwise. Energetically, there is no difference between the two motions, but once you start the wheel spinning in one direction, there is no classical way to get it spinning in the other direction without stopping the wheel first. Quantum mechanically, however, this reversal may be accomplished without first stopping the wheel. In an experiment performed by NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. , in collaboration with researchers from the University of Queensland The University of Queensland (UQ) is the longest-established university in the state of Queensland, Australia, a member of Australia's Group of Eight, and the Sandstone Universities. It is also a founding member of the international Universitas 21 organisation. , Australia, ultra-cold atoms oscillating os·cil·late intr.v. os·cil·lat·ed, os·cil·lat·ing, os·cil·lates 1. To swing back and forth with a steady, uninterrupted rhythm. 2. in optical potential wells were observed to tunnel from one allowed motion to another which was not well connected via a classical pathway classical pathway n. Immunology The activation of complement by an antigen-antibody complex. . Atoms initially loaded into the bottom of the optical potentials were induced to oscillate To swing back and forth between the minimum and maximum values. An oscillation is one cycle, typically one complete wave in an alternating frequency. back and forth. The number of atoms in a particular oscillatory oscillatory characterized by oscillation. oscillatory nystagmus see pendular nystagmus. motion was observed to decrease with time, as a group of atoms oscillating 1800 out of phase with the initial motion began to appear. Eventually, almost all of the atoms end up in the out-of-phase motion but then tunneled back to the initial mode of oscillation. The researchers observed up to eight coherent transfers of atoms back and forth between the two stable motions due to dynamic tunneling, and no atoms were observed to exhibit intermediate motion between the two stable oscillatory motions. The observation of dynamic tunneling in a well characterized atomic system opens the door to future studies on the role of decoherence in quantum phenomena. Such studies are crucial for determining the role of decoherence in quantum information processing systems. The results of the experiment were published in the July 5th issue of Nature. CONTACT: Kris Helmerson, (301) 975-4266; khelmerson@nist.gov. |
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