Quantum computers to keep an eye on

Among schemes to build extraordinarily powerful computers whose calculations depend on quantum properties of particles, an approach using molecules in liquids as information bits has consistently attained a higher level of computing complexity than other designs. Now, a competing method, in which ultracold ions serve as bits, is moving up the problem-solving ladder.

In the Jan. 2 Nature, Stephan Gulde of the University of Innsbruck in

Austria and his colleagues there and at the Massachusetts Institute of Technology report carrying out a computation called the Deutsch-Jozsa algorithm. This quantum calculation evaluates certain mathematical functions in one operation, although a conventional computer would require two. To execute the simple procedure, the researchers used laser pulses, which can control the quantum state of a lone calcium ion.

Liquid-based systems have already mastered algorithms such as Deutsch-Jozsa and others that are more complicated (SN: 1/12/02, p. 31: Liquid computer takes key quantum step). However, Innsbruck’s Jürgen Eschner, a member of the research team, says it’s important that an ion-based system has reached the Deutsch-Jozsa rung because liquid systems aren’t expected to work in quantum-computer designs that include more than a handful of bits. In contrast, Eschner notes, ion-based approaches are more likely to accommodate the tens to hundreds of bits required for building practical computers.

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