Dark Matter, QCD Axions, and the HAYSTAC Detector

Despite many decades of searching, the type of particle that forms galactic halo dark matter, assumed to be the major fraction of the mass of our galaxy, remains unknown. One of the earliest suggestions for a dark matter particle is the Axion which was introduced to solve a problem in the the theory of the strong force, however the technology to detect axions as dark matter at an interesting level of sensitivity did not yet exist in the 1980s. Therefore, most research up to the present has sought particles in the form of weakly interacting massive particles that arise, for example, in the context of supersymmetric theories. The possibilities of the existence of such particles is becoming very limited, due in part to lack of a supersymmetry signal at the LHC, and the extremely small upper limit for the neutron and atomic electric dipole moments that provide further constraints. In the last decade, quantum enhanced measurement techniques have been developed that allow the construction of a galactic axion halo detectors with an interesting level of sensitivity. A review of axion physics is presented, and the HAYSTAC detector that employs a squeezed quantum vacuum state receiver is described.