Rapid High-Fidelity Spin-State Readout in Si/Si-Ge Quantum Dots via rf Reflectometry

Silicon spin qubits show great promise as a scalable qubit platform for fault-tolerant quantum computing. However, fast high-fidelity readout of charge and spin states, which is required for quantum error correction, has remained elusive. Radio-frequency reflectometry enables rapid high-fidelity readout of GaAs spin qubits, but the large capacitances between accumulation gates and the underlying two-dimensional electron gas in accumulation-mode Si quantum-dot devices, as well as the relatively low two-dimensional electron gas mobilities, have made radio-frequency reflectometry challenging in these platforms. In this work, we implement radio-frequency reflectometry in a Si/Si-Ge quantum-dot device with overlapping gates by making minor device-level changes that eliminate these challenges. We demonstrate charge-state readout with a fidelity above 99.9% in an integration time of 300 ns. We measure the singlet and triplet states of a double quantum dot via both conventional Pauli spin blockade and a charge latching mechanism, and we achieve maximum fidelities of 82.9 and 99.0% in 2.08- and 1.6-mu s integration times, respectively. We also use radio-frequency reflectometry to perform single-shot readout of single-spin states via spin-selective tunneling in microsecond-scale integration times.