Princeton researchers claim quantum computing breakthrough
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."
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 assistant professor of electrical engineering who is part of the research team.
For years, teams of scientists have pursued the idea of using quantum mechanics to build a new machine that would revolutionize computing. The goal is not build a faster or more powerful computer, but to build one that approaches problems in a completely different fashion.
"The point of a quantum computer is not that they can do what a normal computer can do but faster; that’s not what they are," said Houck. "The quantum computer would allow us to approach problems differently. It would allow us to solve problems that cannot be solved with a normal computer."
One challenge facing scientists is that the spins of electrons, or any other quantum particles, are incredibly delicate. Any outside influences, whether a wisp of magnetism or glimpse of light, destabilizes the electrons’ spins and introduces errors.
Over the years, scientists have developed techniques to observe spin states without disturbing them. But analyzing small numbers of spins is not enough; millions will be required to make a real quantum processor.
To approach the problem, Petta’s team combined techniques from two branches of science. From materials science, they used a structure called a quantum dot to hold and analyze electrons’ spins. From optics, they adopted a microwave channel to transfer the spin information from the dot.
"The methods we are using here are scalable, and we would like to use them in a larger system," Petta said. "But to make use of the scaling, it needs to work a little better. The first step is to make better mirrors for the microwave cavity."