1. A system for coherent coupling of conventional qubits, the system comprising: first, second, and third Josephson junctions; a superconducting flux qubit that supports clockwise and counterclockwise supercurrents in a superconducting ring defined by the first, second, and third Josephson junctions, the flux qubit having a first basis state that corresponds to the clockwise supercurrent and a second basis state that corresponds to the counterclockwise supercurrent; a first semiconductor coupled to a first superconducting island formed between the first and second Josephson junctions, wherein the first semiconductor provides a first conventional double-dot qubit; and a second semiconductor coupled to a second superconducting island formed between the second and third Josephson junctions, wherein the second semiconductor provides a second conventional double-dot qubit, wherein a joint parity of the first and second qubits is measured via an Aharonov-Casher effect that gives rise to an energy splitting in the flux qubit that depends on a total charge enclosed in a region between the first and third Josephson junctions.