Schematic of the ADMX receiver chain showing the path from the cavity microwave signal at the left to near-audio downconverted signal at the right.
The ADMX receiver is sensitive to 0.01 yoctowatts of power. That's equivalent to less than one axion decay within the cavity per minute.
The ultra-low noise microwave receiver makes the
experiment possible. The dominant background is
thermal noise arising from the cavity and
the receiver electronics. Signals from the cavity are
amplified by an exotic cryogenic Superconducting QUantum Interference
Device (SQUID) amplifier followed by ultralow noise
cryogenic HFET amplifiers. The receiver then
downconverts mirowave cavity frequencies to a a lower frequency
that can be easily digitized and saved.
We have demonstrated that the SQUID amplifier allows for quantum limited power sensitivity. The receiver chain is sensitive to powers smaller than 0.01 yoctowatts; this is the world's lowest-noise microwave receiver in a production environment.