Princeton researchers claim quantum computing breakthrough using micowaves

October 23, 2012 // By Dylan McGrath
Researchers from Princeton University have developed a technique to read spintronic information off electrons, a potential step on the road to quantum computing.

Spintronics—a concept in which information is passed by the spin on electronics rather than their charge— promises to revolutionize the computing industry with smaller, faster and more energy efficient data storage and processing.

The Princeton team, headed by physicist Jason Petta, used a stream of microwave photons to analyze a pair of electrons trapped in a tiny cage called a quantum dot. The microwave stream allowed the scientists to read the spin state of the electrons.

"We create a cavity with mirrors on both ends—but they don't reflect visible light, they reflect microwave radiation," Petta said. "Then we send microwaves in one end, and we look at the microwaves as they come out the other end. The microwaves are affected by the spin states of the electrons in the cavity, and we can read that change."

A circuit uses microwaves to read the quantum state of an electron, a potentially scalable route to developing a quantum computer. Credit: Jason Petta/Princeton University

The apparatus created by Petta's team operates over a little more than one centimeter. But, on a subatomic scale, this distance is vast—the team likened the project to coordinating the motion of a top spinning on the moon with another on the surface of the earth.

"It's the most amazing thing," said Jake Taylor, a physicist at the National Institute of Standards and Technology and the Joint Quantum Institute at the University of Maryland, who worked on the project with the Princeton team. "You have a single electron almost completely changing the properties of an inch-long electrical system."

Petta said his team's finding could eventually allow engineers to build quantum computers consisting of millions of quantum bits, or qubits. So far, quantum researchers have only been able to manipulate small numbers of qubits, not enough for a practical machine.

"The whole game at this point in quantum computing is trying to build a larger system," said Andrew Houck, an