Back in the late 90s, a physicist in Australia put forward a design for a quantum computer. Bruce Kane suggested that phosphorus atoms embedded in silicon would be the ideal way to store and manipulate quantum information.
His idea was that the nucleus of the phosphorus atom could store a single qubit for long periods of time in the way it spins. A magnetic field could easily address this qubit using well-known techniques from nuclear magnetic resonance spectroscopy. That would allow single-qubit manipulations but not two qubit operations because nuclear spins do not interact significantly of each other.