HAYSTAC Phase II: Quantum Detection Technology Enhanced Axion Dark Matter Search

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Astrophysical observations and cosmological data point convincingly to a large component of Cold Dark Matter in the Universe. Weakly interacting massive particles (WIMPs) and axions have been proposed as theoretically favored candidates for dark matter. Despite the strong evidence for the existence of dark matter, neither WIMPs nor axions have been conclusively detected. Dark matter axions may be detected through their conversion into a narrow band Radio Frequency (RF) signal in a microwave-cavity resonator permeated by a magnetic field. Under NSF funding, a Yale-UC Berkeley-University of Colorado Boulder collaboration came together in 2011 to design, build and operate an advanced technology experiment, HAYSTAC, to serve both as an innovation test-bed to develop new cavity designs and quantum-limited photon detection schemes, and as a pathfinder to take first data in the 10 to 50 micro-eV mass range, well above all previous such searches. This award will provide funding to continue this axion search. The collaboration-wide efforts of HAYSTAC are leading to many technical innovations. R&D on superconducting thin-films and sub-quantum-limited photon detection will produce unanticipated spin-offs. The experimental techniques being developed, in particular magnetic shielding and data analysis, will be useful to other experiments that use similar quantum sensing techniques. The group will continue their successful recruiting and training of new talent inclusively. HAYSTAC has been very successful in attracting many bright young people to the field. The PIs are active in giving popular public lectures and participating in educational outreach. Wright Laboratory has begun negotiations with the Peabody Natural History Museum at Yale to prepare an exhibit highlighting the history and research of the Laboratory itself, featuring dark matter studies.HAYSTAC is the first dark matter search to successfully incorporate a squeezed-vacuum-state quantum limited receiver, and along with LIGO, is among the first fundamental physics experiments to use squeezed-state receivers for data production. The actual system noise temperature is twice the standard quantum limit (SQL), with the additional quantum of noise from transmission losses. During Phase I, HAYSTAC established an exclusion limit of 2.3 times the KSVZ coupling at 23.15 to 24.0 micro-eV. HAYSTAC is nearing its goal of increasing the mass scan rate by at least a factor of 2 compared to Phase I, with sensitivity at the level of about twice the KSVZ axion coupling. Additional innovative improvements are planned, including a new symmetrized-tuner design cavity and an improved squeezed state receiver that eliminates losses from circulators and other elements in the present receiver design. A long run will then commence to cover the axion mass range predicted by Klaer and Moore, based on the first and only calculation of axion production incorporating in a self-consistent way both the vacuum realignment and string radiation mechanisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.