Linked particles advance quantum computing

By Eric Smalley, Technology Research News

Researchers have linked a pair of quasi-atoms in a microscopic speck of semiconducting material, a development that brings the far off dream of solid-state quantum computing another step closer.

The research boosts efforts to build quantum computers from quantum dots, which are tiny amounts of semiconductor that allow researchers to contain and manipulate small numbers of atoms and subatomic particles.

In this experiment, researchers used a single quantum dot made of gallium arsenide to entangle a pair of excitons. Excitons are composed of an electron, which is negatively charged, and a positively charged hole in the semiconductor. Ordinarily an electron will fill a positively charged hole, but when an electron and a hole interact without combining an exciton forms.

"It's an electron and a hole that appear to be in orbit around each other," said Duncan G. Steel, professor of physics and electrical engineering and computer science at the University of Michigan. "It's like an atom."

An atom or subatomic particle can serve as a quantum bit, or qubit, because it spins in one of two directions, and those spin directions can represent the ones and zeros of binary computing. Entangling atoms or particles allows multiple qubits to work together, which is a prerequisite for quantum computing.

But entangling a pair of excitons in a quantum dot will not by itself lead to quantum computers.

"It's a baby step," Steel said. "This is not a scalable system. This is the first step in doing something that would be scalable. The plans call for doing this between two or more dots rather than doing it in a single dot, but the physics is similar."

The main challenge to entangling excitons across several quantum dots is being able to make the dots precisely enough to control the interactions between them, Steel said. The researchers might be able to report on this step in about eight months, he said.

Many researchers estimate that it will be at least 20 years before usable quantum computers can be built.

"The problems in implementing quantum computing as it's currently envisioned are very challenging and I don't think any of us are in a position [to] predict when or even if it's going to happen," said Steel.

The enormous number-crunching potential of quantum computers for certain applications, particularly cryptography, make the efforts to build quantum computers well worth while, he added.

The researchers reported their work in the September 15, 2000 issue of the journal Science. Steel's colleagues were Gang Chen and Nicolas H. Bonadeo of the University of Michigan, Daniel G. Gammon, Douglas S. Katzer and Doewong Park of the Naval Research Laboratory, and Lu Jeu Sham of the University of California San Diego.

The research was funded by the National Security Agency, the Advanced Research Development Agency, the Army Research Office, the Air Force Office of Scientific Research, the Office of Naval Research and the National Science Foundation.

Timeline:   Unknown
Funding:   Government
TRN Categories:   Quantum Computing
Story Type:   News
Related Elements:   Technical paper "Optically Induced Entanglement of Excitons in a Single Quantum Dot" in Science September 15, 2000


October 4, 2000

Page One

DNA does logic

Quantum quirk promises smaller circuits

Pop-up book melds real with virtual

Lab-on-a-CD corrects itself

Linked particles advance quantum computing


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