UCLA Engineering: UCLA Engineer Magazine

Quantum Computing, Secure Communications Closer to Reality;
UCLA Scientists Control a Single Electron’s Spin

Professor Eli Yablonovitch

In 2004, a UCLA team of researchers succeeded in flipping a single electron spin upside down in an ordinary commercial transistor chip, and detected current change when the electron flips.

“Our research demonstrates that an ordinary transistor, the kind used in a desktop PC or cell phone, can be adapted for practical quantum computing,” said Hong Wen Jiang, a UCLA professor of physics and member of the California NanoSystems Institute, in whose laboratory the experiments were conducted. The research makes quantum computing closer and more practical.

A single electron spin represents a quantum bit, the fundamental building block of a quantum computer.

Many scientists believe that an exotic new technology would be required for quantum computing. However, Jiang said, “I would not be surprised one day to see a quantum computer built, based almost entirely on silicon technology.”

“We have measured a single electron spin in an ordinary transistor; this means that conventional silicon technology is adaptable enough, and powerful enough, to accommodate the future electronic requirements of new technologies like quantum computing, which will depend on spin,” said electrical engineering professor Eli Yablonovitch, who holds the Northrop Grumman Opto-Electronics Chair in Electrical Engineering.

“We’ve done this with a commercial silicon integrated circuit chip, literally off a shelf,” Yablonovitch said. “Silicon is the dominant technology of our time, and will remain so for some time. For those who think silicon has too many limitations, silicon technology is surprisingly adaptable, enough so to meet the futuristic requirements of the 21st century. In the electronics of the 21st century, we will manipulate single electron spins - not just the charge of the electron, but the spin of the electron.”

When quantum computing becomes a reality, the government may be able to use it to eavesdrop on terrorists and quickly break sophisticated secret codes, said Yablonovitch, director of UCLA’s Center for Nanoscience Innovation for Defense.

Quantum computing will use quantum physics to communicate much more securely; if someone tries to intercept a quantum message, the information would be destroyed, Jiang said.

“With 100 transistors, each containing one of these electrons, you could have the implicit information storage that corresponds to all of the hard disks made in the world this year, multiplied by the number of years the universe has been around,” Yablonovitch said. “And why stop with 100 transistors?”

A next step is to demonstrate the “entanglement” of two spins, where the orientation of one electron determines the orientation of the other - a puzzle identified by Albert Einstein.

In the late 1990s, Yablonovitch formed a team of physicists, engineers, materials scientists and mathematicians to create an electronic device that could some day be used for quantum information processing.

The research, a combination of physics and engineering, was funded by the United States Defense Advanced Research Projects Agency, the United States Defense MicroElectronics Activity and the Center for Nanoscience Innovation for Defense.

Ivar Martin, a theoretical physicist at Los Alamos National Laboratory, is a co-author on the Nature paper announcing the breakthrough.

- Stuart Wolpert

Photo: Reed Hutchinson