High Bandwidth Electron Spin Readout with the Radio Frequency Single Electron Transistor in the Strong Response Regime

Surface code architectures capable of fault tolerant error correction need high fidelity, and high bandwidth qubit state readout to minimise errors. High bandwidth readout enables faster qubit gate operations, greater statistics for experiments involving electron spin readout, and the measurement of faster electron transitions. Collectively these result in lower errors on both measured and idling qubits during readout operations. Previously, electron spin readout fidelities above 99% were achieved with a d.c. single electron transistor (SET) by limiting the bandwidth to 100 kHz. Here we present results of charge and spin readout using a radio frequency SET (rf-SET) which can achieve the strong response regime, in which the SET conductance contrast is large compared to its average conductance. At the rf circuit’s full bandwidth (9.5 MHz) and B=1.5 T, we demonstrate single-shot electron spin readout with a signal-to-noise ratio (SNR) of 7.2. For detection of the electron charge states the SET input power was increased to achieve an SNR of 12.7. Optimised single-shot electron spin readout with readout fidelities above 98% for 50 kHz tunnel rates was found to be limited by the base electron temperature (200 mK) and local heating of the SET by dissipation of the rf power.