Efficient multiqubit entanglement via a spin-bus

We propose an experimentally feasible architecture where controllable long-range couplings between spins are built up from local exchange interactions. The scheme consists of a spin-bus, with strong, always-on interactions, coupled dynamically to external spin qubits. The presence of a spectral gap enables the bus to function as a long-range conduit for spin information. The bus also forms a hub for multiqubit entangling operations. We show how multiqubit gates may be used to efficiently generate $W$-states--an important entanglement resource. In this way, the spin-bus provides an alternate route for scalable solid-state quantum computation, using currently available experimental resources