  Spins based in silicon provide one of the most promising architectures for
quantum computing. Quantum dots are an inherently scalable technology. Here, we
combine these two concepts into a workable design for a silicon-germanium
quantum bit. The novel structure incorporates vertical and lateral tunneling,
provides controlled coupling between dots, and enables single electron
occupation of each dot. Precise modeling of the design elucidates its potential
for scalable quantum computing. For the first time it is possible to translate
the requirements of fault-tolerant error correction into specific requirements
for gate voltage control electronics in quantum dots. We demonstrate that these
requirements are met by existing pulse generators in the kHz-MHz range, but GHz
operation is not yet achievable. Our calculations further pinpoint device
features that enhance operation speed and robustness against leakage errors. We
find that the component technologies for silicon quantum dot quantum computers
are already in hand.
