An 11-qubit atom processor in silicon

Abstract

Phosphorus atoms in silicon represent a promising platform for quantum computing, as their nuclear spins exhibit coherence times over seconds1,2 with high-fidelity readout and single-qubit control3. By placing several phosphorus atoms within a radius of a few nanometres, they couple by means of the hyperfine interaction to a single, shared electron. Such a nuclear spin register enables high-fidelity multi-qubit control4 and the execution of small-scale quantum algorithms5. An important requirement for scaling up is the ability to extend high-fidelity entanglement non-locally across several spin registers. Here we address this challenge with an 11-qubit atom processor composed of two multi-nuclear spin registers that are linked by means of electron exchange interaction. Through the advancement of calibration and control protocols, we achieve single-qubit and multi-qubit gates with all fidelities ranging from 99.10% to 99.99%. By entangling all combinations of local and non-local nuclear-spin pairs, we map out the performance of the processor and achieve state-of-the-art Bell-state fidelities of up to 99.5%. We then generate Greenberger–Horne–Zeilinger (GHZ) states with an increasing number of qubits and show entanglement of up to eight nuclear spins. By establishing high-fidelity operation across interconnected nuclear spin registers, we realize a key milestone towards fault-tolerant quantum computation with atom processors. An 11-qubit atom processor comprising two precision-placed nuclear spin registers of phosphorus in silicon is shown to achieve state-of-the-art Bell-state fidelities of up to 99.5%.