Experiments using laser light and fingernail-sized pieces of gray material may offer clues to a fundamental scientific puzzle: What is the connection between the everyday world of classical physics and the hidden quantum world, which obeys completely different rules?
“We found specific material that sits between the two,” says Peter Armitage, an assistant professor of physics at Johns Hopkins University who published his work in the journal Nature. Six scientists from Johns Hopkins and Rutgers University have been working on materials called topological insulators that can conduct electricity on their atom-thick surface, but not inside.
Topological insulators were predicted in the 1980s, first discovered in 2007 and have been actively studied since then. Composed of hundreds of elements, these materials can exhibit quantum properties that usually only appear at the microscopic level, but still remain visible to the naked eye.
The experiments, which Science has written about, have placed these materials in a separate state of matter that "exhibits macroscopic quantum mechanical effects," Armitage says. “We usually think of quantum mechanics as a theory of small things, but in this system, quantum mechanics manifests itself at macroscopic length scales. The experiments became possible thanks to the unique equipment developed in my laboratory."
As part of the experiments, samples of dark gray material made from elements of bismuth and selenium - each several millimeters in length and of varying thickness - were struck by terahertz light beams that are invisible to the naked eye. The researchers measured the reflected light as it travels through material samples and found prints of the quantum state of matter.
Specifically, they found that when light was passed through the material, the wave exhibited characteristics associated with physical constants that are usually measured only in atomic-scale experiments. These properties were consistent with the predictions made for the quantum state.
These results deepen the understanding of topological insulators and may also contribute to the development of another area, which Armitage calls "the central issue of modern physics." What is the connection between the macroscopic classical world and the microscopic quantum world, from which the first flows?
Since the early 20th century, scientists have tried to understand how one set of physical laws governing objects larger than a certain size can coexist with another set of laws governing atomic and subatomic scales. How does classical mechanics derive from quantum mechanics and where is the threshold that divides these spheres?
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These questions remain to be answered, but topological isolators may be part of the solution.
“It's part of the puzzle,” says Armitage.
ILYA KHEL
