Indirect Interaction of Solid-State Qubits via Two-Dimensional Electron   Gas
  We propose a mechanism of long-range coherent coupling between nuclear spins to be used as qubits in solid-state semiconductor-heterojunction quantum information processing devices. The coupling is via localized donor electrons which in turn interact with the two-dimensional electron gas. An effective two-spin interaction Hamiltonian is derived and the coupling strength is evaluated. We also discuss mechanisms of qubit decoherence and consider possibilities for gate control of the interaction between neighboring qubits. The resulting quantum computing scheme retains all the gate-control and measurement aspects of earlier approaches, but allows qubit spacing at distances of order 100nm, attainable with the present-day semiconductor device technologies. 
Dima Mozyrsky, Vladimir Privman, M. Lawrence Glasser