Electron-nuclear interaction in 13C nanotube double quantum dots

For coherent electron spins, hyperfine coupling to nuclei in the host material can either be a dominant source of unwanted spin decoherence(1-3) or, if controlled effectively, a resource enabling storage and retrieval of quantum information(4-7). To investigate the effect of a controllable nuclear environment on the evolution of confined electron spins, we have fabricated and measured gate-defined double quantum dots with integrated charge sensors made from single-walled carbon nanotubes with a variable concentration of C-13 (nuclear spin I = 1/2) among the majority zero-nuclear-spin C-12 atoms. We observe strong isotope effects in spin-blockaded transport, and from the magnetic field dependence estimate the hyperfine coupling in C-13 nanotubes to be of the order of 100 mu eV, two orders of magnitude larger than anticipated(8,9). C-13-enhanced nanotubes are an interesting system for spin-based quantum information processing and memory: the C-13 nuclei differ from those in the substrate, are naturally confined to one dimension, lack quadrupolar coupling and have a readily controllable concentration from less than one to 10(5) per electron.