Quantum computing depends on how quantum objects can be coupled coherently. To suppress decoherence, many schemes have involved temperatures at millikelvin levels. Now, Torsten Gaebel of the University of Stuttgart and colleagues in Germany, Australia and the US have achieved long-lived coherently coupled spins at room temperature by implanting nitrogen into high-purity diamonds.
The idea is to create pairs of spins that are close enough to be strongly coupled, while being far enough from other spins to avoid decoherence. Gaebel and colleagues embedded N+2 molecular ions into diamond, where the molecules split up to form closely spaced single nitrogen atoms (N). This process also creates vacancies (V) in the diamond lattice, and during annealing at 900 °C the vacancies move and can become trapped next to nitrogen atoms in the diamond lattice to form an NV centre. This has an electron spin, which could be used as a qbit, the basic element of a quantum computer; it also has an optical transition that can be used to control it and read it out.
As the yield of NV centres created is low, the researchers demonstrated the potential of the approach by studying the coherent coupling between NV centres and nearby nitrogen atoms. They found a characteristic decay time for coherence of about 350 ms at room temperature. Already a long time, this seems to be limited only by the carbon-13 content of the diamond. This indicates that an array of NV centres, in principle, could be manipulated optically to build a quantum computer.
Further reading
Torsten Gaebel et al. 2006 Nature Physics 2 408.