A device-friendly qubit?

To be useful for quantum computing, a qubit—a two-level quantum system analogous to the classical bit—must be able to undergo thousands of operations without losing its quantum information to its environment. To survive that long, nearly all solid-state qubits must be chilled to cryogenic temperatures. One exception is an atomic-scale diamond defect known as an NV center—in which a nitrogen atom and a vacancy substitute for neighboring carbon atoms in the crystal lattice. Even at room temperature, the quantum state of an NV center can persist for more than 1 ms, plenty of time to perform useful quantum calculations. But diamond isn’t easily equipped with the logic gates and other components needed to transform a collection of qubits into a working computer. Researchers led by David Awschalom (University of California, Santa Barbara) may have found a way around that problem. They’ve discovered quantum-controllable defects embedded in wafers of a much more device-friendly material—silicon carbide. Using microwave radiation, Awschalom and company were able to coherently control an ensemble of the defects for more than 40 µs at room temperature. That’s conceivably long enough to allow thousands of quantum operations. And like diamond’s NV centers, the spin states of the SiC defects could be both polarized and detected by optical means. Among the researchers’ next priorities are determining the defects’ structure and showing that the defects can be individually manipulated and entangled. (W. F. Koehl et al., Nature 479, 84, 2011.)—Ashley G. Smart