Collaborative Research: HAYSTAC Quantum Enhanced

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Under the award "HAYSTAC Quantum Enhanced", the University of California Berkeley and the University of Colorado participate in one of the forefront experiments in the world seeking to discover the identity of the dark matter of the universe. This experiment searches for a hypothetical elementary particle, called the axion, which is predicted to be extremely light, perhaps a trillionth of the mass of an electron, and extremely weakly interacting. The principle of the experiment is that in the presence of a strong magnetic field, axions can convert to microwave photons, which can be detected by quantum-sensitive amplifiers and receivers. The conversion process can be resonantly enhanced in a tunable microwave cavity; the R&D, production and operation of these microwave cavities is the responsibility of UC Berkeley in the collaboration. The University of Colorado develops the quantum sensors. The other institutions are Johns Hopkins University and Yale University, where the experiment is sited. HAYSTAC has been the world leader in the application of quantum sensing to dark matter searches. Under previous NSF funding, HAYSTAC was the first dark matter experiment to evade a fundamental theorem of quantum mechanics on the irreducible noise of amplifiers, the Standard Quantum Limit, by a sophisticated technique known as squeezed-vacuum states. Discovery of dark matter would constitute a revolution in our understanding of cosmology, and excite generations of young students to pursue careers in physical science and engineering. HAYSTAC has also been a driver for breakthroughs in quantum information science, and advanced microwave concepts, and has generated several Ph.D. students who have gone on to careers in the fields of quantum computing and accelerator science. Under NSF funding, a Yale-Berkeley-Colorado collaboration came together in 2011 to design, build and operate HAYSTAC (now joined by Johns Hopkins), a small experiment serving both as an innovation test-bed to develop new cavity designs and quantum-enhanced photon detection schemes, and as a pathfinder to take first data in the 10–50 micro-eV mass range. Immediately upon commissioning in 2015 with the first-ever use of a Josephson Parametric Amplifier (JPA), HAYSTAC achieved essentially quantum-limited operation. In the past three years, the collaboration successfully implemented a two-JPA squeezed-vacuum state receiver, circumventing the Standard Quantum Limit (SQL) entirely and establishing an exclusion limit around 17 micro-eV; these results being published in Nature in February 2021. HAYSTAC is the only dark matter experiment to employ a squeezed-state receiver (SSR), and along with LIGO one of only two experiments exploiting squeezed states for data production in the world of fundamental physics. In parallel with the development of quantum-enhanced receivers, the collaboration has pursued similar advances in microwave resonators. Under this proposal, the team will complete and analyze the ongoing long run with the current squeezed state receiver, which is operating with a scan rate further improved from the first SSR. Berkeley will then deploy a new and improved symmetrized-tuner design cavity, and another long run will commence to move upwards in frequency toward a recent theoretical prediction. Colorado will develop and test a prototype of their cavity entanglement and state-swapping concept (published in Physical Review X Quantum), which should be complete within this grant period; whereas the current SSR yielded a factor of ×2 in scan rate, this new scheme is expected to produce a ×15 speedup. Colorado and Berkeley will jointly carry out the integration and commissioning in HAYSTAC. Berkeley will continue R&D on Photonic Band Gap resonators for TE-mode suppression, metamaterial resonators to reach much higher frequencies, and continued mitigation of the anomalous thermal noise contribution. Each of these innovations dramatically enhance 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.