Haloscope Searching for Dark Photons at Q-band with a Novel Coupling Tuning Structure

Laboratory searching for dark matter is crucial for understanding several fundamental conundrums in physics and cosmology. Most cavity-based haloscope searches focus on the frequency range below 10 GHz, while the parameter space with higher frequency remains rarely explored, due to the challenges lying in the fabrication of microwave cavities. Here we report the first Q-band haloscope searching for dark photons with a 33.141 GHz cavity. A novel coupling tuning structure separated from the cavity was designed so as not to degrade the quality factor of the cavity. We have established the most stringent constraints $\chi<2.5\times10^{-12}$ at a confidence level of 90$\%$ in the frequency range from 33.139 GHz to 33.143 GHz, corresponding to the mass of dark photons ranging from 137.05 $\mu$eV to 137.07 $\mu$eV. The results surpass the previous astronomical constraints by nearly three orders of magnitude. This work has demonstrated the feasibility of dark matter haloscopes at Q band. In the future, the constraints can be further improved by more than one order of magnitude through low-temperature experiments, and the setup can be extended to search for axions, axion-like particles, and high-frequency gravitational waves.