Two teams have forged the first chip-based version of a quantum bus, a tool for mixing and swapping information between qubits. The bus is a squiggly wire between two superconducting loops, which served as qubits. When activated, a qubit loop transfers its superposition to the wire in the form of a microwave photon. Raymond Simmonds of the National Institute of Standards and Technology in Boulder, Colo., who led one of the teams, got a seven-millimeter-long wire to store a photon for more than one microsecond. Rob Schoelkopf of Yale University and his group performed a similar trick with a longer wire that mixed a single quantum state between two qubits. To make a quantum computer, though, the researchers will have to keep the superconducting qubits stable or coherent for longer periods.
This article was originally published with the title "A Qubit Bus" in Scientific American 297, 6, 38 (December 2007)