Low-magnetic field single-spin qubit operation in isotopically enriched silicon*

Single-spin qubit readout traditionally relies on selective tunneling to a neighboring reservoir. It requires sophisticated microwave engineering to deliver high-frequency qubit drives to the quantum chip from room-temperature electronics, which will be a challenge for scaling of a silicon-based quantum processor. Here we present an alternative scheme where we use high-fidelity Pauli spin blockade readout to enable single-spin qubit operation in a magnetic field as low as 150mT. We discover the qubits decohere faster in low magnetic fields due to the background (800 ppm) ²⁹Si nuclear spins in the isotopically enriched substrate. A simulation modeling the nuclear spin induced qubit frequency fluctuation produced results consistent with our experimental data. This work indicates that further isotopic enrichment may be needed to achieve the high fidelities required for a scalable quantum processor.