Engineering long spin coherence times of holes in silicon

Future quantum technologies require quantum bits that remain coherent over long time scales, a goal recently achieved for electron spins in some semiconductors. Because of their strong spin-orbit coupling, hole-based qubits have attracted interest to achieve long-distance coupling, and to build hybrid quantum systems and spin/photon interfaces. However, it is not known if spin-orbit coupling of holes is compatible with long coherence times, since to date, experimentally reported values are too short for most envisioned applications. Here we show that holes bound to B:Si dopants in 28Si can be engineered to have spin coherence times rivalling electrons in 28Si. The results are obtained by directly controlling spin-phonon coupling and electric dipole components of the qubit responsible for decoherence, by applying a small strain to the silicon lattice. Thereby, we establish hole spins in silicon as a platform with coherence times rivalling electrons, and with tunable intrinsic spin-orbit coupling advantageous to build hybrid quantum systems and couple qubits over long distances.