An 11-qubit atom processor in silicon

TL;DR

This paper reports the development of an 11-qubit silicon-based atom processor utilizing phosphorus nuclear spins, demonstrating high-fidelity multi-qubit control, entanglement, and scalable protocols towards fault-tolerant quantum computing.

Contribution

The work introduces a fully controlled 11-qubit silicon atom processor with scalable calibration, high-fidelity gates, and interconnected nuclear spin registers for quantum error correction.

Findings

Achieved fidelities from 99.5% to 99.99% for quantum gates.

Prepared Bell states with over 99% fidelity.

Generated GHZ states across all data qubits.

Abstract

Phosphorus atoms in silicon are an outstanding platform for quantum computing as their nuclear spins exhibit coherence time over seconds. By placing multiple phosphorus atoms within a radius of a few nanometers, they couple via the hyperfine interaction to a single, shared electron. Such a nuclear spin register enables multi-qubit control above the fault-tolerant threshold and the execution of small-scale quantum algorithms. To achieve quantum error correction, fast and efficient interconnects have to be implemented between spin registers while maintaining high fidelity across all qubit metrics. Here, we demonstrate such integration with a fully controlled 11-qubit atom processor composed of two multi-nuclear spin registers which are linked via electron exchange interaction. Through the development of scalable calibration and control protocols, we achieve coherent coupling between nuclear spins using a combination of single- and multi-qubit gates with all fidelities ranging from 99.5% to 99.99%. We verify the efficient all-to-all connectivity by preparing both local and non-local Bell states with a record state fidelity beyond 99% and extend entanglement through the generation of Greenberger-Horne-Zeilinger (GHZ) states over all data qubits. By establishing high-fidelity operation across interconnected nuclear-spin registers, we realise a key milestone towards fault-tolerant quantum computation with atom processors.