HAYSTAC (Haloscope At Yale Sensitive To Axion Cold dark matter) is a Yale-Berkeley-Colorado-Johns Hopkins collaboration, and represents the latest generation microwave cavity axion experiment. HAYSTAC serves both as a Pathfinder for the 2.5-12 GHz (10-50 ueV) axion mass range, and an Innovation Testbed where the most advanced concepts in ultrasensitive receivers and microwave resonators can be tested in operation. To date it has been the only microwave cavity experiment operating at the Standard Quantum Limit (SQL) of noise. In 2019 it was upgraded with a Squeezed-vacuum State Receiver which circumvents the SQL entirely, and first results have been published in Nature. Berkeley’s role is R&D and production of the microwave cavities.
