A single-atom qubit in silicon

A newly fabricated device can read and write information using the spin of an electron bound to a single atom.

The up or down spin of an electron makes it a natural qubit to use in an eventual quantum computer. One difficulty in any qubit system is preserving the qubits’ fragile phase coherence long enough to perform a sequence of quantum calculations. Another is scalability. For instance, qubits made from isolated atoms offer long coherence times but are hard to scale up into macroscopic devices, whereas those made from bulk semiconductors are scalable but usually suffer from high decoherence rates (see Physics Today, March 2006, page 16). A research group led by Andrea Morello and Andrew Dzurak (both from the University of New South Wales) have now combined the advantages of both architectures by fabricating a qubit based on a single atom’s electron spin.