  The electron spin is a natural two level system that allows a qubit to be
encoded. When localized in a gate defined quantum dot, the electron spin
provides a promising platform for a future functional quantum computer. The
essential ingredient of any quantum computer is entanglement---between electron
spin qubits---commonly achieved via the exchange interaction. Nevertheless,
there is an immense challenge as to how to scale the system up to include many
qubits. Here we propose a novel architecture of a large scale quantum computer
based on a realization of long-distance quantum gates between electron spins
localized in quantum dots. The crucial ingredients of such a long-distance
coupling are floating metallic gates that mediate electrostatic coupling over
large distances. We show, both analytically and numerically, that distant
electron spins in an array of quantum dots can be coupled selectively, with
coupling strengths that are larger than the electron spin decay and with
switching times on the order of nanoseconds.
