[EDP1] SQUID, Detector, Metrology, Novel Device

[EDP1-05] Superconducting quantum capacitance detectors with increased saturation power for 1.6 THz

*Tianyuan Chi¹, Jingbo Wu^1,2, Lili Shi^1,3, Siming Zang¹, Rui Tan¹, Yuwei Zhu¹, Runfeng Su¹, Junhua Chen¹, Xuecou Tu^1,2, Biaobing Jin^1,2, Jian Chen^1,2, Peiheng Wu^1,2 (1. Nanjing Univ. (China), 2. Purple Mountain Lab. (China), 3. NEST (Italy))

Keywords:

Quantum capacitance detectors,Superconducting detectors,Terahertz astronomy,Increased saturation power

Superconducting quantum capacitance detectors (QCDs)¹ have recently emerged as the most sensitive terahertz (THz) single-photon detectors available at millikelvin temperatures, positioning them as leading candidates for the focal-plane instrumentation of next-generation cryogenic space telescopes. Despite their record-breaking noise performance, the practical deployment of QCDs in broadband THz astronomy has been impeded by a restricted saturation power².In this work we introduce and experimentally validate a deterministic control mechanism that enables flexible tuning of the sensitivity and saturation power of the detector by engineering the gate capacitance. The underlying mechanism is derived from the energy level structure of the single cooper-pair box (SCB) and experimentally validated across 0.6 yW to 10 fW with four different detectors. The cryogenic measurements performed confirm that the engineered gate capacitance modulates the tunneling out rate of quasiparticles from superconducting island and the saturation power changed accordingly.Leveraging this strategy, we realize an optimized QCD integrating a fork-shaped gate capacitor for reducing the volume of the superconducting island and a high-efficiency grid absorber for polarization-independent THz photon coupling, as shown in Fig. 1. The device attains a noise-equivalent power (NEP) of 3.7 × 10^-20 W/Hz^1/2 while simultaneously exhibiting a saturation power of 3 fW at 1.6 THz, thereby achieving a balanced operating point that satisfies the sensitivity and dynamic-range requirements of upcoming THz survey missions. These results establish a clear pathway toward the integration of QCDs in large-format focal-plane arrays for future cryogenic THz telescopes.