Quantum computing and single-qubit measurements using the spin filter   effect
  Many things will have to go right for quantum computation to become a reality in the lab. For any of the presently-proposed approaches involving spin states in solids, an essential requirement is that these spins should be measured at the single-Bohr-magneton level. Fortunately, quantum computing provides a suggestion for a new approach to this seemingly almost impossible task: convert the magnetization into a charge, and measure the charge. I show how this might be done by exploiting the spin filter effect provided by ferromagnetic tunnel barriers, used in conjunction with one-electron quantum dots. 
David P. DiVincenzo (IBM)