The first solid state qubit

The proposal of quantum information processing has shown us the first serious possibility, though still limited in applications, to break away from the traditional spell that has been binding integration scale and processing power for some time. The qubit (quantum bit), the basic element of quantum information processing, consists of a quantum two-level system that can be brought to a superposition by an external mean. Among the numerous possible two-level systems, various typical microscopic two-level systems such as nuclear spins and atomic states have been utilized first to demonstrate the realization of quantum calculation. However, to realize a scaled-up version of a quantum computing system consisting of hundreds of qubits, a solid state electronics version of it is considered to be indispensable. We demonstrate the first electronic control of 1-qubit achieved in a solid state device using a submicron electron device called a single-electron box, a small conductive box connected to the outside by a tunnel junction and a gate capacitor. The scalability of such a solid state qubit is considered to be a prerequisite for a practical quantum computer of the future.