November 12, 1998
Vol. 18 No. 4

current issue
archive / search

    Professor talks of physics, scientific dreams of future

    By Steve Koppes
    News Office

    Transporter beams exist only in the Star Trek television series, but Woowon Kang, Assistant Professor in Physics, can produce a similar phenomenon on a minuscule scale in his Chicago laboratory. The phenomenon is called tunneling, a process in which electrons seem to magically flow through barriers instead of bounce off them.

    Kang is co-writing a paper on tunneling as it relates to the quantum Hall effect, a force that governs the behavior of electrons in powerful magnetic fields. His co-author is 1998 physics Nobel laureate Horst Stormer of Columbia University.

    Stormer shared the 1998 Nobel Prize in physics with Chicago alumnus Daniel Tsui, now at Princeton University, and Stanford University’s Robert Laughlin. Kang worked for Stormer from 1992 to 1994 as a postdoctoral researcher at Bell Laboratories, doing follow-up work to the Nobel experiments.

    Supported since 1995 by a $500,000 grant from the David and Lucile Packard Foundation, Kang has expanded his research portfolio. Today, he conducts experiments on tunneling in organic superconductors and on sonoluminescence–the production of light using sound. But all of his research stems from an interest in quantum mechanics, the seemingly mysterious laws of physics that govern the behavior of subatomic particles.

    Scientists at the University of Cologne accidentally discovered sonoluminescence in 1934 while studying bubbles in water. The scientists applied high-intensity sound to water. When they developed a photographic plate of their experiment, they unexpectedly found evidence of flashes of light.

    The phenomenon was largely forgotten until 1992, when University of Mississippi scientists demonstrated how to produce light emission from a single bubble. They injected a bubble into an acoustic chamber filled with water, then applied high-intensity ultrasound. This produced a small bubble of rapidly expanding and contracting gas that emitted a flash of light during each cycle.

    “If you look at the apparatus, you see a glowing ball,” Kang said. The process produces 40,000 flashes each second, which is far too rapid to be detected by the human eye.

    Temperatures inside the bubble reach at least 18,000 degrees Fahrenheit, which in part, accounts for the light, Kang said. No one knows for sure exactly how hot the bubble gets because it has never been directly measured.

    Even though sonoluminescence has been known for years, “the way you produce the light is rather mysterious,” Kang said. Going from low-energy, high-intensity sound to high-energy light in sonoluminescence requires a trillion-fold jump in energy.

    The mystery has attracted increased attention from physicists in recent years. The University’s Materials Research Science and Engineering Center sponsored a Symposium on Sonoluminescence in September 1997.

    Sound is a phenomenon well-explained by classical mechanics, the basic laws of everyday physics. But light photons are governed by quantum mechanical processes.

    “Somehow, you’re going from classical mechanics to quantum mechanics through sonoluminescence,” Kang said. “That means there’s some interesting process going on that’s transforming sound into light.”

    But it remains to be seen whether sonoluminescence is indeed quantum mechanical.

    “Indirectly, one could explain a lot using classical mechanics, but that leaves an empty feeling,” Kang said. “If it turns out to be classical mechanics, it’s still an interesting process, but it’s not going to open new research areas or raise profound questions in physics.”

    If sonoluminescence is quantum mechanical, the evidence is well-hidden. “To prove it’s quantum mechanical will be a rather challenging task. It’s not hopeless, but it’s challenging,” Kang said.

    In 1996, Kang began experimenting with sonoluminescence in a magnetic field. The law of electrodynamics states that light-producing phenomena must involve an acceleration of charged particles.

    “A high magnetic field will bend the motion of the particles, so a magnetic field can, in principle, be useful to study sonoluminescence,” Kang said.

    Kang’s experiments involve a magnetic field 100,000 times more powerful than the Earth’s magnetic field, and from 100 to 1,000 times more powerful than refrigerator magnets. And Kang has found that they do indeed produce a rather strong effect.

    “The question is, what’s producing it?” he asked.

    While sonoluminescence is the latest thrust of Kang’s research, he has been conducting tunneling experiments to learn the properties of organic superconductors in microscopic detail.

    Most organic materials–people, for example–do not conduct electricity. But some organic materials do conduct. And some, when cooled to temperatures slightly above absolute zero, even superconduct, meaning they exhibit no resistance to the flow of electricity.

    Kang uses an experimental material produced via a special electrochemical process in his superconductor research. Under magnification, a few black slivers of the material, which is more expensive than gold, reveal crystals with fine, hexagonal facets.

    Kang hopes that a better understanding of such organic, low-temperature superconductors could aid the development of high-temperature superconductors, those that would operate at room temperature instead of at hundreds of degrees below zero.

    “It’s not clear which material, what research, will eventually give you a room-temperature superconductor,” Kang said. “High-temperature superconductors are one of the most profound mysteries in physics. We’ve made very little headway in their understanding.”

    The low temperatures at which organic superconductors operate limits their technological usefulness, but in the laboratory, it’s an advantage. High temperatures tend to mask the quantum mechanical effects.

    Superconducting technology already is used in magnetic resonance imaging, cellular telephone switching stations and particle accelerators. But with room-temperature superconductors could come faster and more efficient electronic devices and ultra-fast levitating trains that ride frictionless magnets instead of rails.

    “One could imagine many applications, but sometimes, it takes years to get to the stage where they’re technologically viable and economically feasible,” Kang said.

    Such is the nature of science, technology and quantum mechanical transporter beams.

    “It’s amazing the things one can do nowadays that one could only dream about 20 or 30 years ago,” Kang said. “We’re dreaming about Star Trek and transporter beams. Maybe they’ll come true. Who knows? One cannot say that it is impossible.”