Large Scale Modular Quantum Computer Architecture with Atomic Memory and   Photonic Interconnects
  The practical construction of scalable quantum computer hardware capable of executing non-trivial quantum algorithms will require the juxtaposition of different types of quantum systems. We analyze a modular ion trap quantum computer architecture with a hierarchy of interactions that can scale to very large numbers of qubits. Local entangling quantum gates between qubit memories within a single register are accomplished using natural interactions between the qubits, and entanglement between separate registers is completed via a probabilistic photonic interface between qubits in different registers, even over large distances. We show that this architecture can be made fault-tolerant, and demonstrate its viability for fault-tolerant execution of modest size quantum circuits. 
C. Monroe, R. Raussendorf, A. Ruthven, K. R. Brown, P. Maunz, L.-M.   Duan, and J. Kim
quant-ph