Optics research focuses on large scale quantum computing

Stefan Kuhr and scientists from Immanuel Bloch at the Max Planck Institute of Quantum Optics are targeting the best way to realise a quantum computer. The research could address and change the spin of single atoms with laser light and arrange them in arbitrary patterns. The team strung atoms along a line so they could directly observe the tunnelling dynamics in a 'racing duel' of the atoms. According to the researchers, a register of hundreds of addressable quantum particles could serve for storing and processing of quantum information in a quantum computer. Laser cooled rubidium atoms were loaded into an artificial crystal of light. The 'optical lattices' were generated by superimposing several laser beams, with the atoms kept in the lattice of light. Kuhr recently demonstrated that each site of an optical lattice could be filled with exactly one atom. Now, the team says it has succeeded in invidually addressing the atoms in the lattice and changing their respective energy state. Using a microscope, they focused a laser beam down to a diameter of about 600nm and directed it at individual atoms. This slightly deformed each atom's electron shell and changed the energy difference between its two spin states. Kuhr said: "We have shown that we can individually address single atoms. In order for the atom to suit as a quantum bit, we need to generate coherent superpositions of its two spin states. A further step is to realise elementary logical operations between two selected atoms in the lattice, so called quantum gates."