Abstract Body

The terahertz (THz) waveband is of immense interest in astronomy as it encompasses significant energy generated following the Big Bang, offering critical insights into processes invisible in other bands, such as the earliest stages of planet, star, and galaxy formation. Superconducting kinetic inductance detectors (KIDs) have emerged as a formidable contender in the field of THz astronomy, attributed to their exceptional sensitivity and scalability ^[1,2]. In this study, we introduce a novel class of KIDs incorporating a lumped element (LE) superconducting resonator design, with inductors fabricated on β-Ta film and capacitors on α-Ta film. We characterize the noise of the hybrid α-Ta/β-Ta LEKIDs, achieving an optical noise equivalent power (NEP) of 4.8 × 10^-19 W/Hz^1/2, demonstrating high sensitivity (Fig.1). Additionally, the LEKIDs exhibited robust stability across multiple thermal cycles. The combination of high sensitivity and robust stability makes the hybrid LEKIDs promising for the stringent demands of astronomy and other applications at THz waveband.

References

[1] Ulbricht G., De Lucia M. & Baldwin E., Applications for Microwave Kinetic Induction Detectors in Advanced Instrumentation, Appl. Sci., 11, 2671 (2021).
[2] Su R. F., et al. Noise equivalent power of a NbTiN-Al-based kinetic inductance detector for terahertz sensing, Supercond. Sci. Technol., 35, 055016 (2022).

Acknowledgment

This work was supported by the National Key Research and Development Program of China (2021YFB2800701), the National Natural Science Foundation of China (Nos. 62227820, 62035014, 62071217, 62331015).

Figure 1. Measured noise PSD and optical NEP of the hybrid α-Ta/β-Ta LEKID. (a) Measured noise PSD at different radiation powers. The measurements were performed at 60 mK, and the readout power is -100 dBm. The Lorentz fit (dashed line) is used to get the quasiparticle recombination time. The roll-off frequency at higher (lower) and lower (higher) radiation power are shown as the arrows, respectively. (b) Quasiparticle recombination time extracted from the Lorentz fit of (a). The circles denote the measurement data. The blue solid line is a power law fit (P_opt^-0.5), ignoring the data in the saturated regions (the first 14 points). (c) Measured optical NEP of the LEKID at different radiation power. The lowest NEP is 4.8 × 10-¹⁹ W/Hz^1/2. (d) Measured optical NEP at different radiation powers and the calculated photon shot noise with a 43% optical efficiency. The NEP is average between 30 and 50 Hz from (c). The blue star is the measured electrical NEP at 60 mK, which corresponds to a radiation power of 3.4×10^-22 W. The solid green line indicates the calculated photon shot noise with a 43% optical efficiency. The red dashed line is the sum of photon shot noise and G-R noise. The measured NEP is well fitted with the noise limits between 3×10^-17 W and 3× 10^-15 W. After that, the LEKID is gradually saturated, leading to a deviation to the photon shot noise limit.

Keywords: Superconducting detector, Kinetic inductance detector, Photon noise limited sensitivity, Terahertz waveband, Noise equivalent power