Part 7/9:
A significant technical challenge arises from the presence of the naturally occurring silicon-29 isotope, which possesses a nuclear spin and can introduce unwanted variables. Fortunately, silicon-28, an isotope without nuclear spin, provides a promising foundation for qubits. These isotopically purified silicon-28 crystals are being produced for unrelated purposes, namely the Avogadro project, which aims to redefine the kilogram.