The importance of this list is that these are the conventional components of modern silicon chips and there is hope that this proposal, although futuristic and ambitious in many respects, may be facilitated by ongoing developments in silicon fabrication over the next few years. At 100mK, the one outer electron will be weakly bound to the P ion and an electric field applied to the A gate will pull the electron wavefunction away from the donor, reducing the hyperfine interaction and modifying the resonant frequency. Electronic devices for both generating and detecting nuclear spin polarization have been successfully implemented at low temperatures by Kane using GaAs technology although a significant increase in the sensitivity of such devices would be required here. Moreover, in order to isolate the donor dopant nuclear spin it is necessary to use pure spin 0 semiconductor isotopes. This rules out GaAs and directs our attention to silicon, which could, in principle, be purified to contact only spin 0 isotopes.
Quantum computation requires two qubit controlled rotations in addition to single qubit operations.
This requires coupling between two donor-electron spin systems. This allows electron-mediated nuclear spin coupling to occur over comparable distances. Kane presents some estimates of the various relevant parameters and details the operations required to realize a Controlled NOT gate. He also considers the magnitude of the spin decoherence introduced by the gates as well as from other sources of spin dephasing. Charge fluctuations arising from fluctuating occupancies of surface states, for example, are likely to be particularly important.