研究目的
Developing large area cryogenic light detectors for background suppression in neutrinoless double beta decay searches, specifically aiming for a 5 × 5 cm2 detector with 20 eV RMS resolution using phonon-mediated kinetic inductance detectors.
研究成果
The CALDER project has successfully developed phonon-mediated kinetic inductance detectors, achieving a noise energy resolution of 25 eV RMS with AlTiAl multi-layer chips. This progress supports the goal of background suppression in neutrinoless double beta decay experiments. Future work will focus on scaling to 5 × 5 cm2 substrates and mitigating vibration sensitivity, with potential applications in experiments like CUPID.
研究不足
The detectors are sensitive to mechanical vibrations, particularly in silicon substrates, which can degrade performance. The scalability to larger areas (5 × 5 cm2) is still under investigation, and results from this phase are preliminary. The phonon collection efficiency is relatively low (around 10% for aluminum resonators), and the technology requires cryogenic temperatures, limiting practical applications.
1：Experimental Design and Method Selection:
The project is divided into three phases: optimization of aluminum resonators, development of multi-layer titanium-aluminum resonators for improved sensitivity, and scaling to a 5 × 5 cm2 substrate. Kinetic Inductance Detectors (KIDs) are used for their energy resolution and multiplexed read-out capabilities, with a phonon-mediated approach where photons interact with a substrate to produce phonons absorbed by KIDs.
2：Sample Selection and Data Sources:
Substrates include silicon (2 × 2 cm2 and 5 × 5 cm2, 300 μm thick), silicon on sapphire (SOS), and germanium on sapphire (GeOS). Superconducting materials tested are aluminum and AlTiAl multi-layers. Data is collected from light pulses using a 400 nm LED and X-rays from 55Fe for energy calibration.
3：List of Experimental Equipment and Materials:
Equipment includes a 3He/4He dilution refrigerator for cooling to 10 mK, a CITLF4 SiGe low noise amplifier, optical fibers, LED light source, and X-ray sources. Materials involve silicon substrates, aluminum films (60 nm thick), titanium films, and multi-layer superconductors.
4：Experimental Procedures and Operational Workflow:
Detectors are cooled in the dilution refrigerator. Light or X-ray pulses are directed onto the substrate, and the response is measured via the KID output amplified and read out. Noise and energy resolution are evaluated, with optimization for maximum signal-to-noise ratio in the phase direction.
5：Data Analysis Methods:
Energy resolution is calculated based on noise measurements and phonon collection efficiency. Statistical analysis of signal and noise spectra is performed, with cross-calibration using optical and X-ray sources.
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