  Some of the stable isotopes of silicon and carbon have zero nuclear spin,
whereas many of the other elements that constitute semiconductors consist
entirely of stable isotopes that have nuclear spins. Silicon and diamond
crystals composed of nuclear-spin-free stable isotopes (Si-28, Si-30, or C-12)
are considered to be ideal host matrixes to place spin quantum bits (qubits)
for quntum computing and sensing applications because their coherent properties
are not disrupted thanks to the absence of host nuclear spins. The present
article describes the state-of-the-art and future perspective of silicon and
diamond isotope engineering for development of quantum information processing
devices.
