Two Worlds in One?

It's no surprise that quantum physics can be disorienting to the casual observer; after all, it does follow its own set of rules quite different from those of classical physics which rule over our everyday experience. In the quantum realm, things can and cannot be at the same time (to a certain extent) or are continually moving without spending energy. These don't apply to the physics of macro-level matter.

These two realms are related, in so far as they occur in the same physical space. This relationship is what N. Peter Armitage, an associate professor of physics at Johns Hopkins University, wanted to figure out in a study published in the journal Science. "We found a particular material that is straddling these two regimes," Armitage said.

A team of six scientists from Johns Hopskins and Rutgers University studied a material called topological insulators. These were first studied in 2007, but theoretically predicted in the 1980s. These insulators are remarkable because they conduct electricity on their thin-as-an-atom surfaces but not in their insides, plus they have a capacity to display quantum properties.

Consolidating Worlds

Quantum physics deals with atomic and sub-atomic particles and, as already mentioned, display its own unique set of properties. "Usually we think of quantum mechanics as a theory of small things, but in this system quantum mechanics is appearing on macroscopic length scales," explained Armitage. But these topological insulators, as observed in their experiments, "[exhibit] macroscopic quantum mechanical effects," he added.

They used Terahertz (THz) light beams invisible to the naked eye on dark gray material samples of bismuth and selenium. The reflected light measured off these materials showed fingerprints of a quantum state of matter — as the light passed through the material, the wave generated rotation amounts usually only measurable on atomic scale experiments. The physical constants should only be possible in a quantum state.

The experiment itself does not really answer how the relationship between the classical physics and the quantum realm — how two sets of rules applying to the material world exists, separated only by the size of matter. It's a question that's scientists have struggled with since the early 20th century.

One thing's for sure, though: topological insulators may be part of the solution. "It's a piece of the puzzle," Armitage said. And with a puzzle as big (or small) as quantum physics, we'll take whatever piece we can get.

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