Characterizing the dark count rate of a large-format MKID array.

Area of Science:

• Astrophysics
• Detector Physics

Background:

• Large-format arrays of Microwave Kinetic Inductance Detectors (MKIDs) are crucial for astronomical observations, including those at observatories like Subaru.
• Understanding detector noise, specifically the dark count rate, is essential for experiments requiring high sensitivity and low background noise.

Purpose of the Study:

• To empirically measure the dark count rate in a large-format MKID array.
• To assess the suitability of MKIDs for low-count rate applications such as dark matter direct detection.
• To characterize the sources of dark counts in MKID detectors.

Main Methods:

• Measurement of dark count rate across a 0.946-1.534 eV (1310-808 nm) bandpass using a large-format MKID array.
• Analysis of dark count rates in five equal-energy bins to assess spectral dependence.
• Utilizing lower-noise readout electronics for single-pixel MKID characterization.
• Distinguishing dark count events from known light sources and cosmic ray interactions.

Main Results:

• An average dark count rate of (1.847 ± 0.003) × 10⁻³ photons/pixel/s was measured across the 0.946-1.534 eV bandpass.
• Dark count rates varied spectrally, with lower rates observed at higher energies, e.g., (2.73 ± 0.02) × 10⁻⁴ photons/pixel/s at 1.416-1.534 eV.
• Single-pixel measurements with low-noise electronics yielded a dark count rate of (9.3 ± 0.9) × 10⁻⁴ photons/pixel/s, with events attributed to cosmic rays and substrate phonons.

Conclusions:

• MKID arrays exhibit low dark count rates, demonstrating their potential for sensitive experiments like dark matter direct detection.
• The characterization of dark count events suggests contributions from real photons, cosmic ray-induced fluorescence, and phonon interactions.
• Further optimization with low-noise electronics can enhance MKID performance in low-background environments.