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

Understand

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.