All-electrical manipulation of silicon spin qubits with tunable spin-valley mixing

We show that the mixing between spin and valley degrees of freedom in a silicon quantum bit (qubit) can be controlled by a static electric field acting on the valley splitting Delta. Thanks to spin-orbit coupling, the qubit can be continuously switched between a spin mode (where the quantum information is encoded into the spin) and a valley mode (where the quantum information is encoded into the valley). In the spin mode, the qubit is more robust with respect to inelastic relaxation and decoherence but is hardly addressable electrically. It can, however, be brought into the valley mode for electrical manipulation, then back to the spin mode. This opens new possibilities for the development of robust and scalable, electrically addressable spin qubits on silicon. We illustrate this with tight-binding simulations on a so-called "corner dot" in a silicon-on-insulator device for which the confinement and valley splitting can be independently tailored by front and back gates.