In the basement of Princeton’s Hoyt Laboratory, Alexei Tyryshkin clicked a computer mouse and sent a burst of microwaves washing across a silicon crystal suspended in a frozen cylinder of stainless steel. The waves pulsed across the crystal and, deep within it, billions of electrons started spinning at once.
Synchronizing the movement of 100 billion infinitesimal particles is an impressive achievement on its own, but it also is a stride toward developing the technology for quantum computers. These powerful machines could be used to factor incredibly large numbers, break cryptographic codes or simulate the behavior of molecules.
“Standard computers have come to their limit and cannot do some of the things we want,” said Tyryshkin, a research scientist in the Department of Electrical Engineering. “We are trying to find a different way of doing computing, using additional degrees of freedom involving quantum computing and things like spins.”
A fundamental property of electrons, spin offers a path to developing a machine that would apply the realitybending rules of quantum mechanics to arrive at new and powerful ways to approach difficult mathematical problems. But maintaining control over particle spin for long enough to build a working computer has proven difficult.
Until recently, the best attempts at such control lasted for only a fraction of a second. But the work by Tyryshkin and other Princeton researchers, led by Professor of Electrical Engineering Stephen Lyon, revealed a way to extend control over the spins of billions of electrons for up to ten seconds. The work, part of an international effort, was reported online in December 2011 in the journal Nature Materials, and was supported by the National Science Foundation and the U.S. National Security Agency.
The key to these results lay in the use of a highly purified sample of silicon, Lyon said. The experiment uses a small silicon chip the size of a pencil lead made almost entirely of a particular isotope of silicon, silicon-28. To achieve their results, the researchers suspended the sample of pure silicon inside a cylinder filled with liquid helium, and dropped the temperature to 2 degrees Kelvin (-455.8 degrees Fahrenheit, just above absolute zero). They locked the cylinder between two doughnut-shaped rings about the size of pizza boxes that control the magnetic field around the sample. Tyryshkin’s mouse click sent microwaves through the silicon, and coordinated the spins of about 100 billion electrons.
“Partly, it is an improvement in our measurements, but it is mainly the material,” Lyon said. “This is the purest sample we have ever used.”