A Superconducting 2D PCB Resonator for CRES Noise Model Measurements

The Project 8 experiment seeks to measure the neutrino mass through Cyclotron Radiation Emission Spectroscopy (CRES). To do so, the proposed Low-Frequency Apparatus (LFA) demonstrator will operate at 560 MHz. While low-noise measurements necessitate cryogenic temperatures, the large scale of the LFA cavity makes cooling below ~4 K costly and impractical. To overcome thermal noise limitations, we propose using radiative cooling, where the resonant mode of the cavity is strongly overcoupled to a milliKelvin-cooled amplifier. This process effectively lowers the photon population in the electromagnetic mode of the cavity, and hence the thermal noise of the microwave readout.

To validate this noise model and readout chain at 560 MHz, while avoiding the prohibitively difficult construction of a full-scale cavity, a superconducting 2D printed circuit board (PCB) resonator will be constructed as an analog. This resonator will mimic the critical RF parameters (f0, Q0, Qe) of the full-scale LFA cavity. Additionally, it will be equipped with a port for coupling to a Josephson Parametric Amplifier (JPA) cooled to mK temperature and a weakly coupled input for injecting calibrated, CRES-like signals. This presentation details the design of the PCB resonator and the experimental setup, the primary goals of which are to achieve a conclusive validation of the radiative cooling principle and provide a path towards refining signal reconstruction algorithms.