High Bandwidth Electron Spin Readout with the Radio Frequency Single Electron Transistor

Mr Daniel Keith
4pm Thursday 2 November 2017
CQC2T Conference Room, Level 2, Newton Building J12, UNSW Kensington Campus

Qubit state readout is an essential step for quantum computation and must introduce minimal errors if full error correction is to be achieved with a surface code architecture. The lowest errors during readout will only be possible if the readout is not only high fidelity, but also high bandwidth. Typically, for electron spin qubits in Si-P donor based systems, a single electron transistor (SET) is used as a charge sensor to perform single-shot electron spin readout. Previously, spin readout fidelities above 99% have been achieved with a dc measured SET, but only by limiting the bandwidth to 100 kHz [1].
Here, we demonstrate using a radio frequency SET (rf-SET) and characterize its bandwidth, shot-noise and readout fidelity. At the full bandwidth of the rf-SET circuit, 9.5 MHz, we demonstrate single-shot electron spin readout at B=1.5 T with an effective signal-to-noise ratio of 7.2. For electron charge state detection the power broadening is no longer limited by the electron spin state splitting, allowing us to achieve an effective signal-to-noise ratio of 12.7 by increasing the driving power before being limited by heating of the rf-SET. Optimized single-shot readout of electrons, with 50 kHz tunnel rates, achieved measurement fidelities above 98% limited by the base electron temperature (200 mK).
Importantly, we have shown that the high bandwidth readout has multiple benefits: it enables the measurement of faster electron transitions, has greater statistics for experiments employing electron spin readout, and faster qubit gate operations. Collectively these lead to lower errors on both measured and idling qubits during readout operations.

[1] Watson, et al., Phys. Rev. Lett. 115, 166806 (2015)