Operating semiconductor quantum processors with hopping spins

Abstract

Qubits that can be efficiently controlled are essential for the development of scalable quantum hardware. Although resonant control is used to execute high-fidelity quantum gates, the scalability is challenged by the integration of high-frequency oscillating signals, qubit cross-talk, and heating. Here, we show that by engineering the hopping of spins between quantum dots with a site-dependent spin quantization axis, quantum control can be established with discrete signals. We demonstrate hopping-based quantum logic and obtain single-qubit gate fidelities of 99.97%, coherent shuttling fidelities of 99.992% per hop, and a two-qubit gate fidelity of 99.3%, corresponding to error rates that have been predicted to allow for quantum error correction. We also show that hopping spins constitute a tuning method by statistically mapping the coherence of a 10–quantum dot system. Our results show that dense quantum dot arrays with sparse occupation could be developed for efficient and high-connectivity qubit registers. Editor’s summary Several platforms have been developed for quantum computing. These approaches are based on ion traps, neutral atoms, superconducting qubits, and semiconducting qubits. They operate by resonant qubit control, which typically requires high-frequency, complex signals, resulting in detrimental effects such as qubit cross-talk and severe heating. Wang et al. demonstrate a platform for quantum computing that can be operated using discrete and digital control pulses only. Using a small array of quantum dots, they show that spin states can be moved from one dot to another with what is in effect a nudge and a hop. Extending the effect to a larger array demonstrates the ability to process quantum information on what can be a simpler platform requiring lower hardware overhead. —Ian S. Osborne