Preserving coherence long enough to perform meaningful calculations is one of the major challenges on the pathway to large-scale quantum-computer implementations. Noise coupled in from the environment is the main factor contributing to decoherence but can be mitigated via engineering design and control solutions. However, this is possible only after acquisition of a thorough understanding of the dominant noise sources and their spectrum. In the work reported here, we use a silicon quantum dot spin qubit as a metrological device to study the noise environment experienced by the qubit. We compare the sensitivity of this qubit to electrical noise with that of an implanted silicon-donor qubit in the same environment and measurement setup. Our results show that, as expected, a quantum dot spin qubit is more sensitive to electrical noise than a donor spin qubit due to the larger Stark shift, and the noise-spectroscopy data show pronounced charge-noise contributions at intermediate frequencies (2–20 kHz).

A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits.