  An infinite array of parallel current-carrying wires is known, from the field
of neutral particle optics, to produce an exponentially localized magnetic
field when the current direction is antiparallel in adjacent wires. We show
that a finite array of several tens of superconducting Nb nanowires can produce
a peak magnetic field of 10mT that decays by a factor of 10^4 over a length
scale of 500nm. Such an array is readily manufacturable with current
technology, and is compatible with both semiconductor and superconducting
quantum computer architectures. A series of such arrays can be used to
individually address single single-spin or flux qubits spaced as little as
100nm apart, and can lead to quantum logic gate times of 5ns.
