Scientists have come closer to fast quantum computers made of atoms trapped by beams of light, thanks to the first images of the individual atoms in such a grid.

Quantum computers get their speed because their components can occupy a range of states rather than just two as in a binary computer, reports New Scientist.

Special algorithms can exploit these quantum states to solve problems that would defeat a conventional computer.

One candidate for such a computer is a so-called optical lattice, in which ultracold atoms are coaxed by strategically placed laser beams into a grid arrangement, rather like eggs in an egg carton. But before we can read and write to these atoms, which will be necessary if the lattice is to act as a quantum computer, their precise positions need to be determined.

Now two teams, one led by Stefan Kuhr of the Max Planck Institute for Quantum Optics in Garching, Germany, the other by Markus Greiner of Harvard University, have taken a first step by imaging the individual rubidium atoms in an optical lattice. This is a challenge not just because the atoms are tiny, but also because photons from nearby atoms can interfere with each other, smearing out any pattern.

To overcome this, the teams studied the light pattern from a single atom.

They then created an algorithm which could generate a composite of this pattern from different arrangements of a grid of atoms. By matching these simulations to the actual pattern seen, the algorithm could determine the arrangement of atoms. Each atom in the lattice would act as a quantum bit. Mr. Kuhr says that the optical lattice has many more of these “qubits” than other approaches to quantum computing, and so could offer greater speed.

The study has been published in Nature.