The QCD axion, which solves the strong CP problem in QCD, is one of the best motivated dark-matter candidates. I will discuss efforts to develop electromagnetic searches for QCD axion dark matter with masses below 1 micro-eV, including the Dark Matter Radio Cubic Meter experiment, which will probe the QCD axion band over 1.5 orders of magnitude in axion mass. However, full coverage of the QCD axion band will not be possible without acceleration by using quantum measurement techniques, which can be used to evade the standard quantum limit by the exploitation of quantum correlations in the electromagnetic signals. While photon counting is a useful technique to evade the SQL at masses above 1 micro-eV, it is not a useful technique at lower mass ranges. I will describe Quantum Upconverters, which convert signals from DC up to ~300 MHz to the microwave frequency range. Quantum upconverters can be used to implement techniques including backaction evasion to outperform the Standard Quantum Limit at the RF frequencies probed by DM Radio. They can also be used to improve electromagnetic sensing of nuclear spins for NMR-based detection schemes (including CASPEr).
(This seminar series is sponsored by Ginzton Laboratory, SPRC, Applied Physics, Physics, and HEPL)