Single holes confined in semiconductor quantum dots are a promising platform for spin-qubit technology, due to the electrical tunability of the g factor of holes. However, the underlying mechanisms that enable electric spin control remain unclear due to the complexity of hole-spin states. Here, we study the underlying hole-spin physics of the first hole in a silicon planar metal-oxide-semiconductor (MOS) quantum dot. We show that nonuniform electrode-induced strain produces nanometer-scale variations in the heavy-hole–light-hole (HH-LH) splitting. Importantly, we find that this nonuniform strain causes the HH-LH splitting to vary by up to 50% across the active region of the quantum dot. We show that local electric fields can be used to displace the hole relative to the nonuniform strain profile, allowing a mechanism for electric modulation of the hole g tensor. Using this mechanism, we demonstrate tuning of the hole g factor by up to 500%. In addition, we observe a potential sweet spot where dg(11¯0)/dV=0, offering a configuration to suppress spin decoherence caused by electrical noise. These results open a path towards a technology involving engineering of nonuniform strains to optimize spin-based devices.

Valence band holes confined in silicon quantum dots are attracting significant attention for use as spin qubits. However, experimental studies of single-hole spins have been hindered by challenges in fabrication and stability of devices capable of confining a single hole. To fully utilize hole spins as qubits, it is crucial to have a detailed understanding of the spin and orbital states. Here we show a planar silicon metal-oxide-semiconductor-based quantum dot device and demonstrate operation down to the last hole. Magneto-spectroscopy studies show magic number shell filling consistent with the Fock–Darwin states of a circular two-dimensional quantum dot, with the spin filling sequence of the first six holes consistent with Hund’s rule. Next, we use pulse-bias spectroscopy to determine that the orbital spectrum is heavily influenced by the strong hole–hole interactions. These results provide a path towards scalable silicon hole-spin qubits.

Silicon quantum dot spin qubits provide a promising platform for large-scale quantum computation because of their compatibility with conventional CMOS manufacturing and the long coherence times accessible using 28Si enriched material. A scalable error-corrected quantum processor, however, will require control of many qubits in parallel, while performing error detection across the constituent qubits. Spin resonance techniques are a convenient path to parallel two-axis control, while Pauli spin blockade can be used to realize local parity measurements for error detection. Despite this, silicon qubit implementations have so far focused on either single-spin resonance control, or control and measurement via voltage-pulse detuning in the two-spin singlet-triplet basis, but not both simultaneously. Here, we demonstrate an integrated device platform incorporating a silicon metal-oxide-semiconductor double quantum dot that is capable of single-spin addressing and control via electron spin resonance, combined with high-fidelity spin readout in the singlet-triplet basis.

The understanding of weak measurements and interaction-free measurements has greatly expanded the conceptual and experimental toolbox to explore the quantum world. Here we demonstrate single-shot variable-strength weak measurements of the electron and nuclear spin states of a P31 single-atom donor in silicon. We first show how the partial collapse of the nuclear spin due to measurement can be used to coherently rotate the spin to a desired pure state. We explicitly demonstrate that phase coherence is preserved with high fidelity throughout multiple sequential single-shot weak measurements and that the partial state collapse can be reversed. Second, we use the relation between measurement strength and perturbation of the nuclear state as a physical meter to extract the tunnel rates between the P31 donor and a nearby electron reservoir from data conditioned on observing no tunneling events. Our experiments open avenues to measurement-based state preparation, steering and feedback protocols for spin systems in the solid state, and highlight the fundamental connection between information gain and state modification in quantum mechanics.

We define single electron spin qubits in a silicon metal-oxide-semiconductor double quantum dot system. By mapping the qubit resonance frequency as a function of a gate-induced electric field, the spectrum reveals an anticrossing that is consistent with an intervalley spin-orbit coupling. We fit the data from which we extract an intervalley coupling strength of 43 MHz. In addition, we observe a narrow resonance near the primary qubit resonance when we operate the device in the (1,1) charge configuration. The experimental data are consistent with a simulation involving two weakly exchanged-coupled spins with a Zeeman energy difference of 1 MHz, of the same order as the Rabi frequency. We conclude that the narrow resonance is the result of driven transitions between the T- and T+ triplet states, using an electron spin resonance signal of frequency located halfway between the resonance frequencies of the two individual spins. The findings presented here offer an alternative method of implementing two-qubit gates, of relevance to the operation of larger-scale spin qubit systems.