Spin relaxation of a donor electron coupled to interface states
Peihao Huang, Garnett W. Bryant
An electron spin qubit in a silicon donor atom is a promising candidate for quantum information processing because of its long coherence time. To be sensed with a single-electron transistor, the donor atom is usually located near an interface, where the donor states could also be coupled with interface states. Here we study the possible spin relaxation mechanisms arising from the coupling of a donor to confined interface states. We find that both Zeeman interaction and spin-orbit interaction can hybridize spin and orbital states, and lead to phonon-assisted spin relaxation for donors coupled to interface states in addition to the spin relaxation for a single donor in bulk silicon. The spin relaxation due to Zeeman interaction and spin-orbit interaction show the same $B^5$ dependence on the magnitude of the applied magnetic field, but show different angular dependencies on the orientation of the applied magnetic field. We find that there are peaks in the B-dependent spin relaxation (spin relaxation hot spots) due to strong hybridization of orbital states with opposite spin. We also find spin relaxation dips (spin relaxation cool spots) due to the interference of different spin relaxation paths. Qubit operation for B near a dip may be used for the preservation of quantum information during the transfer of spin qubit between donor atoms via interface states.