Sensitive radio-frequency read-out of quantum dots using an ultra-low-noise SQUID amplifier

Schupp, F J and Vigneau, F. and Wen, Yutian and Mavalankar, A and Griffiths, J. P. and Jones, G. A. C. and Farrer, I. and Ritchie, David and Smith, C. G. and Camenzind, L. C. and Yu, L. and Zumbühl, Dominik and Briggs, G. Andrew D. and Laird, Edward (2020) Sensitive radio-frequency read-out of quantum dots using an ultra-low-noise SQUID amplifier. Journal of Applied Physics, 127: 244503. ISSN 0021-8979

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Abstract

Fault-tolerant spin-based quantum computers will require fast and accurate qubit readout. This can be achieved using radio-frequency reflectometry given sufficient sensitivity to the change in quantum capacitance associated with the qubit states. Here, we demonstrate a 23-fold improvement in capacitance sensitivity by supplementing a cryogenic semiconductor amplifier with a SQUID preamplifier. The SQUID amplifier operates at a frequency near 200 MHz and achieves a noise temperature below 600 mK when integrated into a reflectometry circuit, which is within a factor 120 of the quantum limit. It enables a record sensitivity to capacitance of 0.07 aF/ \sqrt{Hz}. The setup is used to acquire charge stability diagrams of a gate-defined double quantum dot in a short time with a signal-to-noise ration of about 38 in 1 μs of integration time.