Improving Signal to Noise Ratio Improvement Characterization for the Axion Dark Matter Experiment

The Axion Dark Matter eXperiment searches for the weak signal of axion dark matter decaying to photons in a microwave cavity. Using a dilution refrigerator and quantum amplifiers, we have reached sub-Kelvin noise temperature. In the recent data taking runs the gains of the quantum amplifiers, Josephson parametric amplifiers (JPA), have been vulnerable to environmental factors, causing noticeable changes in the noise temperature over short time scales. Signal to noise ratio improvement (SNRI) is an important metric to track the noise temperature in-situ. Currently, SNRI is one of ADMX's dominant sources of uncertainty. We propose a new method for calculating the SNRI by comparing noise power spectra, containing multiple injected tones, with the JPA pump on and off. This method gives an SNRI measurement that is more robust to unstable JPA gains and may substantially reduce the downtime of JPA-related operation.