Collaborative Research: HAYSTAC Sub-Quantum

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

All astrophysical and cosmological data now point convincingly to a large component of Cold Dark Matter in the Universe, whose presence we only infer gravitationally. A well-motivated candidate for Dark Matter is a light axion. Axions have been introduced to explain the smallness of the violation of the Charge-Parity (CP) symmetry in Quantum ChromoDynamics, the theory describing the action of the strong force. Dark matter axions may be detected through their conversion into a narrow Radio Frequency (RF) signal in a microwave-cavity resonator permeated by a magnetic field. This Yale-Berkeley-Colorado collaboration came together 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 - 50 micro-eV mass range, well above all previous such searches for axions. R&D on superconducting thin-films, and sub-quantum-limited photon detection will certainly produce unanticipated spin-offs, just as the NSF-supported development of the Microstrip SQUID Amplifier for axions did in the quantum information world. HAYSTAC has already proven to be a great attractor for young talent, more than half being women; this award can only be expected to extend this record. In addition, it is planned to establish a rotating exhibit on dark-sector science at the San Francisco Exploratorium utilizing prototypes and artifacts from many of the historic dark sector and cosmic microwave background experiments. Short of finding the axion, HAYSTAC has been extraordinarily successful. During the past three-year period, the experiment has achieved essentially quantum-limited operation (no other experiment has come within an order of magnitude). In preparation for Phase II, Berkeley has designed and built a microwave cavity with a high figure of merit for the 6 - 12 GHz range (~ 25 - 50 micro-eV). Colorado has designed, built and characterized a squeezed-vacuum state receiver, now being commissioned in HAYSTAC - it will be the first-ever sub-quantum receiver for a dark-matter experiment, and with LIGO the first squeezed-state receivers for data production in the world of fundamental physics. Furthermore, the group will produce a first cavity prototype incorporating planar thin-films of NbTiN, a Type-II superconductor, to achieve a boost in quality factor Q by an order of magnitude, a gain that would map directly into mass scan rate. Each of these innovations dramatically enhances the discovery potential of HAYSTAC. 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.