Speaker
Description
Microwave cavity-based dark matter axion searches are presented with two challenges to achieving credible discovery potential. The first, common to searches at all axion masses, is achieving the requisite sensitivity, which has been a driver for quantum sensing. The HAYSTAC experiment has been a leader in the development of superconducting devices for the post-inflation axion, including the flux-pumped Josephson Parametric Amplifier which enabled the first quantum-limited dark matter axion search, and a squeezed-state receiver which circumvented the Standard Quantum Limit entirely, increasing its scan rate by a factor of two. An even more powerful scheme, two-cavity entanglement and state exchange has been demonstrated on the bench and is being prepared for operation next year. The second challenge is extending the mass (frequency) range upward or downward to where conventional microwave cavities are no longer viable. Pushing up further into the post-inflation mass range, the ALPHA experiment will incorporate a wire-array metamaterial resonator whose plasma frequency can be designed for the 10-50 GHz range with large volume. At sufficiently high frequencies, owing to the density of wire elements, metamaterial resonators will need to be superconducting to achieve a suitably high quality factor, for which an active R&D program is ongoing.