Quantum Sensing for Fundamental Physics
Prof. Dr. Claudio Gatti (Frascati, Italy)

Quantum Sensing for High Frequency Gravitational Waves and Axion Dark Matter: Microwave cavities in strong magnetic fields are among the most promising tools for detecting dark-matter axions and high-frequency gravitational waves. These searches rely on the Primakoff and Gertsenshtein effects, which predict the conversion of axions and gravitational waves, respectively, into electromagnetic radiation in the presence of a strong static magnetic field. In a microwave cavity, this interaction leads to the displacement of the vacuum state of the resonant mode, generating a coherent electromagnetic signal. Given the expected signal weakness, developing detectors with sensitivity beyond the quantum limit is crucial. In the C and X bands of the electromagnetic spectrum, superconducting qubits have demonstrated exceptional performance for this purpose. However, strong magnetic fields pose challenges, requiring either signal transport to a shielded region or the use of magnetically resilient devices. Additionally, qubit state readout errors due to noise and dephasing limit sensitivity. These challenges can be mitigated through quantum non-demolition measurements, either by repeating the measurement over time or employing multiple qubits simultaneously. During the seminar, we will discuss ongoing developments at the COLD laboratory of the INFN Frascati National Laboratories, focusing on non-demolitive measurement techniques and the development of magnetically resilient qubits.

1. R. Moretti et al., “Transmon qubit modeling and characterization for Dark Matter search,” arXiv:2409.05988.
2. A. Rettaroli et al. “Novel two-qubit microwave photon detector for fundamental physics applications,” Nuclear Instruments and Methods in Physics Research A 1070 (2025) 170010.
3. A. D’Elia et al. “Characterization of a Transmon Qubit in a 3D Cavity for Quantum Machine Learning and Photon Counting,” Appl. Sci. 2024, 14(4), 1478.
4. QUAX Collaboration “Search for axion dark matter with the QUAX–LNF tunable haloscope” Phys. Rev. D 110, 022008 (2024).