A solid-state quantum computing structure includes a d-wave superconductor in
sets
of islands that clean Josephson junctions separate from a first superconducting
bank. The d-wave superconductor causes the ground state for the supercurrent at
each junction to be doubly degenerate, with two supercurrent ground states having
distinct magnetic moments. These quantum states of the supercurrents at the junctions
create qubits for quantum computing. The quantum states can be uniformly initialized
from the bank, and the crystal orientations of the islands relative to the bank
influence the initial quantum state and tunneling probabilities between the ground
states. A second bank, which a Josephson junction separates from the first bank,
can be coupled to the islands through single electron transistors for selectably
initializing one or more of the supercurrents in a different quantum state. Single
electron transistors can also be used between the islands to control entanglements
while the quantum states evolve. After the quantum states have evolved to complete
a calculation, grounding the islands, for example, through yet another set of single
electron transistors, fixes the junctions in states having definite magnetic moments
and facilitates measurement of the supercurrent when determining a result of the
quantum computing.