endo-Fullerene and doped diamond nanocrystallite-based models of qubits for solid-state quantum computers.

Models of encapsulated nuclear spin 1/2 1H and 31P atoms in fullerene and diamond nanocrystallite, respectively, are proposed and examined with an ab initio local density functional method for possible applications as single quantum bits (qubits) in solid-state quantum computers. A 1H atom encapsulated in a fully deuterated fullerene, C20D20, forms the first model system and ab initio calculation shows that the 1H atom is stable in its atomic state at the center of the fullerene with a barrier of about 1 eV to escape. A 31P atom positioned at the center of a diamond nanocrystallite is the second model system, and 31P atom is found to be stable at the substitutional site relative to interstitial sites by 15 eV. Vacancy formation energy is 6 eV in diamond, so the substitutional 31P atom will be stable against diffusion during the formation mechanisms within the nanocrystallite. The coupling between the nuclear spin and the weakly bound (valance) donor electron in both systems is found to be suitable for single qubit applications, whereas the spatial distributions of (valance) donor electron wave functions are found to be preferentially spread along certain lattice directions, facilitating two or more qubit applications. The feasibility of the fabrication pathways for both model solid-state qubit systems within practical quantum computers is discussed within the context of our proposed solid-state qubits.