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.