  We describe a technique for quantum information processing based on localized
en sembles of nuclear spins. A qubit is identified as the presence or absence
of a collective excitation of a mesoscopic ensemble of nuclear spins
surrounding a single quantum dot. All single and two-qubit operations can be
effected using hyperfine interactions and single-electron spin rotations, hence
the proposed scheme avoids gate errors arising from entanglement between spin
and orbital degrees of freedom. Ultra-long coherence times of nuclear spins
suggest that this scheme could be particularly well suited for applications
where long lived memory is essential.
