Electron’s quantum behavior recorded by lasers


Researchers say they've come up with a way to record and control behavior of a single electron at the quantum mechanical level, which could bring quantum computing and information processing one step closer.

A research team headed by University of Chicago scientists reports using laser light in ultrafast pulses to control the quantum state of electrons contained inside nanoscale defects located in a diamond, and also observe changes in that electron over a period of time.

The researchers focused on the quantum mechanical property of electrons knows as spin.

In a manner similar to the way conventional computers hold bits of data, either a binary 1 or 0, in an electron's charge state, in a quantum-based computer spin states of individual electrons would represent a quantum bit, dubbed a qubit.

At the center of the team's research, reported in the online journal Science Express, is a quantum spin system known as a nitrogen-vacancy center, an atomic-scale defect found naturally occurring in diamonds.

In an NV center, a single nitrogen atom sits adjacent to an empty point in the diamond's crystalline latticework.

"These defects have garnered great interest over the past decade, providing a test-bed system for developing semiconductor quantum bits as well as nanoscale sensors," says research head David Awschalom, a molecular engineering professor at Chicago. "Here, we were able to harness light to completely control the quantum state of this defect at extremely high speeds."

The researchers were able to illuminate a single such NV center with two pulses of light from a laser, each less than a millionth of a millionth of a second.

The quantum state of the electron bound within the defect is excited by the first pulse, switching states in a characteristic way, then is stopped by the second pulse.

The time period between the first and second pulse is critical, since the electron will interact with its local surroudings in characteristic way determined by that timescale, the researchers said.

Testing the electron's reaction to a wide number of different pulse timescale can yield a representation of the quantum dynamics of an NV center that is much better than has ever been obtained before, the researchers said.

"Our goal was to push the limits of quantum control in these remarkable defect systems," says study participant and co-author Lee Bassett, now a Universty of Pennsylvania electrical engineering professor, "but the technique also provides an exciting new measurement tool."

The findings could be an important milestone on the road to quantum computing, other scientists not involved in the study say, moving beyond just the simple observation of a quantum state controlling materials at the atomic level.

"This technique also provides a means of control of the spin state -- an important precursor for any quantum information system," says Evelyn Hu, a Harvard University professor of electrical engineering and physics.

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