The isolation of qubits from noise sources, such as surrounding nuclear spins and spin-electric susceptibility , has enabled extensions of quantum coherence times in recent pivotal advances towards the concrete implementation of spin-based quantum computation. In fact, the possibility of achieving enhanced quantum coherence has been substantially doubted for nanostructures due to the characteristic high degree of background charge fluctuations . Still, a sizeable spin-electric coupling will be needed in realistic multiple-qubit systems to address single-spin and spin-spin manipulations . Here, we realize a single-electron spin qubit with an isotopically enriched phase coherence time (20 μs) and fast electrical control speed (up to 30 MHz) mediated by extrinsic spin-electric coupling. Using rapid spin rotations, we reveal that the free-evolution dephasing is caused by charge noise-rather than conventional magnetic noise-as highlighted by a 1/f spectrum extended over seven decades of frequency. The qubit exhibits superior performance with single-qubit gate fidelities exceeding 99.9% on average, offering a promising route to large-scale spin-qubit systems with fault-tolerant controllability.

This is the first experimental demonstration of a fault-tolerant spin qubit in industry-compatible isotopically natural silicon.

We demonstrate a new method for projective single-shot measurement of two electron spin states (singlet versus triplet) in an array of gate-defined lateral quantum dots in GaAs. The measurement has very high fidelity and is robust with respect to electric and magnetic fluctuations in the environment. It exploits a long-lived metastable charge state, which increases both the contrast and the duration of the charge signal distinguishing the two measurement outcomes. This method allows us to evaluate the charge measurement error and the spin-to-charge conversion error separately. We specify conditions under which this method can be used, and project its general applicability to scalable quantum dot arrays in GaAs or silicon.

We extract the phase coherence of a qubit defined by singlet and triplet electronic states in a gated GaAs triple quantum dot, measuring on time scales much shorter than the decorrelation time of the environmental noise. In this nonergodic regime, we observe that the coherence is boosted and several dephasing times emerge, depending on how the phase stability is extracted. We elucidate their mutual relations, and demonstrate that they reflect the noise short-time dynamics.

In conventional measurements of the resistance of a two-dimensional (2D) layer an electrical current is driven through the layer and the voltage drop along the layer is measured. In contrast, Coulomb drag studies are performed on two closely spaced but electrically isolated layers, where a current I 1 is driven through one of the layers (active layer) and the voltage drop V 2 is measured along the other (passive) layer (Fig. 1). The origin of this voltage is electron-electron (e-e) interaction between the layers, which creates a 'frictional' force that drags electrons in 1