Exchange-controlled single-electron-spin rotations in quantum dots

We show theoretically that arbitrary coherent rotations can be performed quickly (with a gating time ~1 ns) and with high fidelity on the spin of a single confined electron using control of exchange only, without the need for spin-orbit coupling or ac fields. We expect that implementations of this scheme would achieve gate error rates on the order of \eta ~ 10^{-3} in GaAs quantum dots, within reach of several known error-correction protocolsComment: 4+ pages, 3 figures; v2: Streamlined presentation, final version published in PRB (Rapid Comm.

Leakage-current lineshapes from inelastic cotunneling in the Pauli spin blockade regime

We find the leakage current through a double quantum dot in the Pauli spin blockade regime accounting for inelastic (spin-flip) cotunneling processes. Taking the energy-dependence of this spin-flip mechanism into account allows for an accurate description of the current as a function of applied magnetic fields, gate voltages, and an inter-dot tunnel coupling. In the presence of an additional local dephasing process or nonuniform magnetic field, we obtain a simple closed-form analytical expression for the leakage current giving the full dependence on an applied magnetic field and energy detuning. This work is important for understanding the nature of leakage, especially in systems where other spin-flip mechanisms (due, e.g., to hyperfine coupling to nuclear spins or spin-orbit coupling) are weak, including silicon and carbon-nanotube or graphene quantum dots.Comment: 11 pages, 10 figures; v2: Typos corrected, colorbar added to fig. 7, final version published in Phys. Rev.