Physicist finds new method for quantum Hall effect

Research conducted by physics professor Zahid Hasan — in collaboration with researchers from Penn, UC Berkeley and institutions in Germany and Switzerland — may bring quantum computers one step closer to some lucky student’s dorm room.

Today’s computers store information with binary logic and, therefore, have a fairly limited memory. Quantum computers would use the spins of electrons to store greater amounts of information.

“When we say electron spin, the electron does not actually rotate,” Hasan said. The electron spin orientation refers instead to the way electrons behave like tiny bar magnets with a north and south pole, he explained, adding that since each electron has two possible spin orientations, there are four possible spin combinations. A logic based on these spin combinations will be more complex than binary logic, he added, and more information would be stored on a quantum computer than on a binary computer.

Hasan said he and his colleagues were very “excited” about their research and its implications in moving computers away from binary logic.

“In … [the] world there’s not just yes or no, there’s possibilities in between,” Hasan said. To make computers respond to logic that is not simply binary, the computer must understand quantum logic, he noted, also explaining that this could only be accomplished by extending quantum logic and the rules of quantum mechanics to the macroscopic world.

“When we think of quantum mechanics, we think of rules that govern microscopic objects,” Hasan said. “It’s very rare that we see the rules … appear in macroscopic object[s].”

These rules manifest themselves in the macroscopic world, but only in a few circumstances, as in the case of the quantum Hall effect, Hasan said. The effect arises when electrons are influenced by very strong magnetic fields and begin to orbit the magnetic field in quantized steps.

The quantum Hall effect is “difficult to use for technology,” Hasan said, as it can only be achieved by cooling metal down to “near absolute zero” and applying a magnetic field equivalent in strength to roughly “10,000 refrigerator magnets.”

Hasan and his team are about to change that.

Drawing on the positive relationship between the speed of an electron and its ability to generate a magnetic field, Hasan said he believes he may be able to achieve the quantum Hall effect without an incredibly strong magnet.

“Maybe if I can move the electrons very fast, it can realize [the] quantum Hall effect … by itself,” Hasan said.

To obtain electrons that can travel extremely quickly, the researchers used the semi-metals antimony and bismuth. In these materials, the desired electron speeds can be achieved, Hasan explained. In examining the behavior of the electrons in these materials, Hasan said he found what he was looking for.

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“I could see electrons that were moving in a way that looks like the quantum Hall effect,” he said.

To further test his theory, Hasan examined materials whose electrons move more slowly. “In those materials, the electrons don’t show [the] quantum Hall effect,” he added.

Achieving this effect without a magnet not only brings quantum computers one step closer to reality, but also creates a great deal of excitement in the physics community.

“It’s like magic with physicists,” Hasan said, adding that the prevailing opinion before his findings was that “you can’t get [the] quantum Hall effect without a magnetic field.”