%0 Journal Article %J Physical Review Letters %D 2015 %T Tunable Spin Qubit Coupling Mediated by a Multi-Electron Quantum Dot %A V. Srinivasa %A H. Xu %A J. M. Taylor %X We present an approach for entangling electron spin qubits localized on spatially separated impurity atoms or quantum dots via a multi-electron, two-level quantum dot. The effective exchange interaction mediated by the dot can be understood as the simplest manifestation of Ruderman-Kittel-Kasuya-Yosida exchange, and can be manipulated through gate voltage control of level splittings and tunneling amplitudes within the system. This provides both a high degree of tuneability and a means for realizing high-fidelity two-qubit gates between spatially separated spins, yielding an experimentally accessible method of coupling donor electron spins in silicon via a hybrid impurity-dot system. %B Physical Review Letters %V 114 %P 226803 %8 2015/06/04 %G eng %U http://arxiv.org/abs/1312.1711v3 %N 22 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.114.226803