Abstract:
The axion is a well-motivated solution to the strong charge–parity (CP) problem in quantum chromodynamics (QCD), and also a natural dark matter candidate. It remains undetected due to its extremely weak coupling to matter required by QCD models and a wide range of allowed masses. The ongoing haloscope experiments such as ADMX and HAYSTAC, which operate between 500 MHz and 5 GHz, are sensitive at the level of yoctowatts. The field is working on extending axion searches out to 50 GHz with a similar sensitivity. High-lying Rydberg states with principal quantum numbers n=60-90 are well suited to microwave detection between 10 - 50 GHz. According to recent theory predictions, this is a very probable mass range for a certain cosmological scenario. Motivated by the potential of using potassium Rydberg atoms as sensitive microwave probes in high-mass haloscope searches, we carried out spectroscopy based on electromagnetically induced transparency (EIT) in a heated vapor cell for high-lying Rydberg levels with n=50-90. In this talk, I will discuss our spectroscopy experiment as a step toward state preparation and other experimental considerations for Rydberg atom-based microwave sensors.