Radio-frequency reflectometry of a quantum dot using an ultra-low-noise SQUID amplifier

• Main Authors: Schupp, F. J, Vigneau, F, Wen, Y, Mavalankar, A, Griffiths, J, Jones, G. A. C, Farrer, I, Ritchie, D. A, Smith, C. G, Camenzind, L. C, Yu, L, Zumbühl, D. M, Briggs, G. A. D, Ares, N, Laird, E. A
• Format: Journal Article
• Language: English
• Published: 29-06-2020
• Subjects: Physics - Applied Physics; Physics - Instrumentation and Detectors; Physics - Mesoscale and Nanoscale Physics; Physics - Quantum Physics
• DOI: 10.48550/arxiv.1810.05767

Journal of Applied Physics 127 244503 (2020) 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 microsecond of integration time.