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Description
We report the QUAX haloscope improvements for the search of post-inflationary QCD axions at about $10\,$GHz frequency. With respect to previous QUAX results, a wide-tuning system is introduced and proved to work in a quasi-automatic protocol.
The haloscope resonator is a cylindrical copper cavity with a sapphire inner cylinder, which allows for a higher effective volume compared to an empty cavity resonating at the same frequency.
Through a clamshell-like mechanism, the cavity can be opened to change the frequency from 10.212 GHz to 10.154 GHz without significantly impacting the quality factor of its axion-sensitive TM030 mode.
The readout chain, using a traveling wave parameter amplifier as the first stage of amplification is devised to work near to the standard quantum limit. With the usage of an $8\,$T magnet, the haloscope is able, in one hour of acquisition, to probe post-inflationary QCD axion models at $10^{-14}\,$GeV$^{-1}$ level in the range $42 - 42.2\,\mu$eV.
With these improvements, QUAX paved the way for a tunable haloscope with QCD axion models' sensitivity in the $9-11\,$GHz frequency range.
