Coherent spin-valley oscillations in silicon

Electron spins in silicon quantum dots are excellent qubits because they have long coherence times and high gate fidelities and are compatible with advanced semiconductor manufacturing techniques. For qubits based on single spins, electron spin resonance with real or effective time-varying magnetic fields is the standard method for universal quantum control. Here we show that spin-valley coupling in Si, which drives transitions between states with different spin and valley quantum numbers, enables coherent control of single-and multi-electron spin states without oscillating electromagnetic fields. We demonstrate Rabi oscillations between effective single-spin states in a Si/SiGe double quantum dot that are driven by spin-valley coupling. Together with the exchange coupling between neighbouring electrons, spin-valley coupling also enables universal control of effective two-spin states, driving singlet-triplet and triplet-triplet oscillations that feature coherence times on the order of microseconds. Our results establish spin-valley coupling as a promising mechanism for coherent control of qubits based on electron spins in semiconductor quantum dots.