Atoms as the smallest quantum bits.

Quantum computers could perform calculations that today's machines can only dream of-if only quantum computers themselves weren't dreams. Still, researchers are beginning to develop ways to encode quantum bits and combine them into logic gates. Arrays of these gates form the basis of computer chips.

Christopher Monroe of the National Institute of Standards and Technology in Boulder, Colo., described a scheme to use single atoms as the bits in a quantum computer. He and his colleagues have demonstrated that they can trap a beryllium ion electromagnetically (SN: 5/25/96, p. 325). When a combination of fast laser pulses excites that ion, it flouresces, emitting photons. The wavelength of these photons indicates the state of a simple logic gate.

Teams doing research on quantum computation have approached the problem from different angles. Neil A. Gershenfeld of the Massachusetts Institute of Technology also presented his group's recent work on using nuclear magnetic resonance (NMR) to create quantum bits among groups of molecules in a liquid (SN: 1/18/97, p. 37). Although the single-atom approach is more flexible, Gershenfeld says, the NMR approach should enable his group to achieve a 10-quantum-bit system by summer. "If we can demonstrate quantum computation, that's all we need."

All lines of research should contribute to a greater understanding of the problem, the scientists say. According to Monroe, "we need at least another decade to understand the limits of quantum computation."