Isotopically engineered Si and Ge for spintronics and quantum computation

Si, Ge as well as SiGe structures are the promising materials for spintronics and quantum computation due to the fact that in both crystals only one isotope ( 29 Si and 73 Ge) has nuclear spin. As a result, isotope engineering of Si and Ge permits to control the density of nuclear spins and vary the spin coherence time, a crucial parameter in spintronics. In the first part we discuss the NMR study of nuclear spin decoherence in Ge single crystals with different abundance of the 73 Ge isotope. It was observed that the slow component of the dephasing process is elongated with depletion of Ge crystal with isotope 73 Ge. The second part is devoted to the development of the Kane's model of nuclear spin-based quantum computer, which uses the nuclear spin of 31 P impurity atoms in a 28 Si matrix as quantum bits (qubits). We discuss a new method of placing 31 P atoms in a 28 Si based on neutron-transmutation-doping of isotopically engineered Si and Ge. In the proposed structure, interqubit coupling is due to indirect hyperfine interaction of 31 P nuclear spins with electrons localized in a 28 Si quasi-one-dimensional nanowire, which allows one to control the coupling between distant qubits.