1. A circuit comprising: a primary compound Josephson junction structure comprising two parallel current paths that are each formed of a material that is superconducting below a critical temperature, wherein each of the two parallel current paths of the primary compound Josephson junction structure includes a respective Josephson junction structure; and wherein the Josephson junction structure in a first one of the two parallel current paths of the primary compound Josephson junction structure includes a first secondary compound Josephson junction structure comprising two parallel current paths that are each formed of a material that is superconducting below a critical temperature, and at least two Josephson junctions, each of which interrupts a respective one of the two parallel current paths of the first secondary compound Josephson junction structure.