On quantum and classical computing with arrays of superconducting persistent current qubits

A superconducting qubit (or quantum bit), which consists of a micrometer-sized loop with three or four Josephson junctions, has two persistent currents of opposite direction as its two states. The states of the qubits, manipulated with magnetic fields and measured with a SQUID, can be brought into quantum coherence to perform quantum computing. Classical bits can also be obtained from these superconducting loops by increasing its critical current, making it possible to base a processor array architecture on these cubits (quantum bits used in a classical way). Such a classical computer might also serve as pre and post processor for the quantum computing performed in the heart of the array. Because classical and quantum computing based on the same device can be studied now simultaneously, architecture of arrays of qubits and cubits seems a good vehicle for studying the quantum computer paradigm, independently from the question whether superconducting loops will be the ultimate implementation vehicle. Other (e.g. spin-based) devices may be more successful. In this paper, the architectural issues of a heterogeneous quantum/classical computer for an implementation of Shor's factoring algorithm based on arrays of qubits and cubits, are presented.