Spin-dependent recombination - an electronic readout mechanism for solid   state quantum computers
  It is shown that coherent spin motion of electron-hole pairs localized in band gap states of silicon can influence charge carrier recombination. Based on this effect, a readout concept for silicon based solid-state spin--quantum computers as proposed by Kane is suggested. The 31P quantum bit (qbit) is connected via hyperfine coupling to the spin of the localized donor electron. When a second localized and singly occupied electronic state with an energy level deep within the band gap or close to the valence edge is in proximity, a gate controlled exchange between the 31P nucleus and the two electronic states can be activated that leaves the donor-deep level pair either unchanged in a |T->-state or shifts it into a singlet state |S>. Since the donor deep level transition is spin-dependent, the deep level becomes charged or not, depending on the nuclear spin orientation of the donor nucleus. Thus, the state of the qbit can be read with a sequence of light pulses and photo conductivity measurements. 
Christoph Boehme and Klaus Lips