  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.
