Experimental demonstration of enhancement in sensitivity to axionic dark matter using a squeezed state receiver*

D. A. Palken, M. Malnou, L. R. Vale, G. C. Hilton, and K. W. Lehnert$\backslash $Squeezed states of the microwave field can be used to reduce the noise in haloscope-based axion detection of the type performed by HAYSTAC [1, 2]. Using a Josephson parametric amplifier (JPA), we generate a squeezed state, inject it into an overcoupled dummy axion cavity, and, upon readout with a second JPA, observe significant improvement in the contrast of a pseudo-axion tone above a background of vacuum noise. We then characterize the time to infer the presence or absence of a weak pseudo-axion signal, and how this time is reduced with squeezing. $\backslash $[1] Zheng, H. \textit{et al.} Preprint at https://arxiv.org/abs/1607.02529 (2016).2] Brubaker, B. \textit{et al}. First Results from a Microwave Cavity Axion Search at 24 $\mu $eV. \textit{Phys. Rev. Lett.} \textbf{118}, 061302 (2017).