Fast charge sensing in undoped silicon quantum dots with radio-frequency reflectometry

Fast and sensitive charge sensing is an essential ingredient in quantum dot (QD) based spin qubit experiments. A performance of the charge sensing can be drastically improved by embedding the sensor in a radio-frequency (rf) tank circuit [1]. While the technique is commonly used in depletion-mode devices, applying it to accumulation-mode devices is a challenge due to a large parasitic capacitance by accumulation gates [2]. In this presentation, we report how to reduce this capacitance and realize charge sensing by the rf reflectometry in undoped Si/SiGe QDs. To this end, we introduce a specially designed device geometry comprising a small accumulation gate area [3]. We observe that the reflected rf power changes more than 30 dB by modulating the sensor conductance, which allows sensitive charge sensing. We achieve single-shot singlet-triplet readout with a SNR of 6 in an integration time of 0.8 μs.

References:
[1] D. J. Reilly et al., Appl. Phys. Lett. 91, 162101 (2007).
[2] C. Volk et al., Nano. Lett. 19, 5628-5633 (2019).
[3] A. Noiri et al., arXiv:1910.03282.