Scalable entanglement of nuclear spins mediated by electron exchange

The use of nuclear spins for quantum computation is limited by the difficulty in creating genuine quantum entanglement between distant nuclei. Current demonstrations of nuclear entanglement in semiconductors rely on coupling the nuclei to a common electron, which is not a scalable strategy. In this work, we demonstrated a two-qubit controlled-Z logic operation between the nuclei of two phosphorus atoms in a silicon device, separated by up to 20 nanometers. Each atom binds separate electrons, whose exchange interaction mediates the nuclear two-qubit gate. We prepared and measured a nuclear Bell state with a fidelity of ${76}_{-5}^{+5}\%$ and a concurrence of ${0.67}_{-0.05}^{+0.05}$. With this method, future progress in scaling up semiconductor spin qubits can be extended to the development of nuclear spin–based quantum computers.