Stephen Lyon, Department of Electrical Engineering, Princeton University

Title:  "Electron Spin Quantum Bits in Silicon"   (video)

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.