Title: "Electron Spin Quantum Bits in Silicon"

Abstract: Many physical systems have been suggested as quantum bits (qubits) for
constructing quantum information processors.  I will discuss recent work
aimed at using the spins of electrons bound to donor impurities and
confined in quantum dots in silicon.  Silicon can be isotopically
enriched and chemically purified such that coherence times exceeding a
second have been experimentally demonstrated.  Bismuth impurities are
particularly interesting, because the large nuclear spin (I=9/2) and
hyperfine interaction between the Bi nucleus and the electron bound to
it lead to "clock states" with inherently long coherence.  One of the
major challenges of using spin-based qubits is controlling the
interactions between spins, which are necessary for 2-qubit gates.
Using bismuth donors, the delicate 2-qubit entangling operations can be
executed entirely on the donor using microwave ENDOR pulses.  Only
operations which simply swap spin states are needed between adjacent
qubits, and these can be mediated by electron spins in nearby quantum
dots.  I will show that this coupled donor/quantum dot system can lead
to a surface code architecture for constructing a quantum information
processor, without requiring atomic-level precision of the placement of
the donor atoms in the Si lattice.