Sheng-Cai Shi

Microwave kinetic inductance detectors (MKIDs) employ arrays of notch-type resonators coupled to a common feedline, enabling frequency-division multiplexing in which the transmission spectrum ( S 21 ) encodes the parameters of all resonators in a single measurement. Accurately extracting individual resonator characteristics—namely, the resonant frequency ( f r ), intrinsic quality factor ( Q i ), coupling quality factor ( Q c ), and asymmetry angle ( ϕ )—remains a major challenge. Traditional single-resonator fitting methods often yield inaccurate results due to severe localized baseline distortions and parameter degeneracies within narrow frequency windows. In this work, we introduce a novel, global fitting algorithm for the scalable and fully automated characterization of large-format resonator arrays. Compared to conventional isolated fitting approaches, our method offers two crucial advantages: (1) it definitively breaks the ambiguity between electrical delay ( τ ) and localized phase asymmetry by simultaneously optimizing over the full wideband spectrum, accurately resolving the delay and dynamic nonlinear baselines; and (2) it introduces a physically-motivated soft shared regularization for Q i . This soft constraint stabilizes the fit by pulling Q i toward a global consensus based on the uniform substrate loss, while still gracefully accommodating natural, fabrication-induced variations. Importantly, this shared regularization inherently forces noise-induced spurious peaks to adopt unphysical Q c values, providing a powerful self-correcting diagnostic that autonomously filters out false candidates. Experimental validation on a 157-pixel MKID array demonstrates highly reliable parameter extraction, yielding a converged Q i ≈ 118   648 ± 40   323 and a log-normal distribution of Q c with median values of 50 720 that matches lithographic design targets. This physically rigorous, detector-agnostic framework overcomes severe baseline ripples and manual threshold tuning, establishing a robust foundation for the rapid, high-throughput characterization of next-generation superconducting arrays.

This study explores the influence of microbridge dimensions on the electrical properties of superconducting titanium (Ti) bolometers. Devices with microbridge sizes ranging from 1 μm tttttttt 1 μm to 32 μm × 32 μm were fabricated and characterized. Resistance-temperature (R-T) measurements show that the critical temperature of the bolometers increases as the microbridge length decreases below 2 μm, corresponding to a length up to approximately 20 times the coherence length and 870 times the electron mean free path. This behavior is attributed to the longitudinal proximity effect. Analysis of the current-voltage (I-V) characteristics measured at different bath temperatures shows that the thermal conductance does not scale linearly with the microbridge area. This nonlinearity is likely caused by incomplete suppression of electron diffusion by the superconducting niobium (Nb) contacts as the Ti film thickness exceeds the proximity length within the Ti layer. This result suggests that optimizing the Ti film thickness could suppress electron diffusion and improve the overall performance of superconducting Ti bolometers.

A terahertz (THz) waveguide directional coupler with weak coupling based on a single quartz chip is proposed in this letter. Three radial microstrip probes are adopted to offer a weak coupling, meanwhile corrugated structures are used to prevent the crosstalk between probes. Both probes and decoupling circuits have been integrated on the single quartz chip to replace the un-machinable waveguide branches in a traditional weak coupler. Besides, the angle and radius of each radial probe can be adjusted to obtain different coupling coefficients. Two quartz chip prototypes with different coupling coefficients of −20 and −17 dB have been produced and mounted in the WR-3.4 waveguide blocks. The measured coupling coefficients are $-18$ ±2 dB and $-15$ ±2 dB, respectively, which agree well with the simulation across the wideband of 200–290 GHz. This exploitation of a single quartz chip with adjustable coupling has exemplified the innovation of weak coupler design, which can meet the application requirements of THz sideband-separating receivers.

We report the observation of discrete supercurrent suppression steps arising from quantum Cooper-pair tunneling in superconductor-graphene-superconductor (SGS) Josephson junctions under near-infrared illumination. This quantum phenomenon remains robust against variations in photon energy, optical power, bath temperature, and dc bias. The nearly identical step spacing observed in SGS Josephson junctions with different graphene channel lengths indicates the dominant role of the superconductor-graphene interface in governing Cooper-pair transport. In contrast, the discrete steps vanish in the negative differential resistance regime, where quasiparticle transport dominates, confirming their microscopic Cooper-pair tunneling origin.

Superconducting transition-edge sensors (TESs) with high sensitivity can detect electromagnetic wave radiations from millimeter/submillimeter, optical to x/γ rays, and have been successfully used in many fields. To improve detection efficiency and sensitivity, large-scale TES arrays are required in combination with multiplexing readout electronics. Compared to other multiplexing schemes, microwave SQUID multiplexing (μMUX), consisting of high-quality microwave superconducting resonators and RF SQUIDs, is most suitable since it provides a wider bandwidth (GHz) and consequently higher multiplexing factor. We designed two types of circuits with different mutual inductances (${{M}_{\mathrm{T}}}$) between the resonator and the RF SQUID: 2.3 pH for the weak-coupling channel and 6.5 pH for the strong-coupling channel. The resonator and RF SQUID washers made of 150 nm Nb are first fabricated by magnetron-sputtering and reactive ion etching, followed by the deposition of Nb/Al–AlOx/Nb trilayer and definition of the Josephson junctions of the RF SQUIDs. This work presents a μMUX demonstration chip with five channels with ${{Q}_{\mathrm{l}}}$ values of 787 and 3626, and the measured frequency shifts ($\Delta {{f}_{\text{pp}}}$) of ∼500 kHz and 4 MHz for the weak- coupling and strong-coupling channels, respectively. The open-loop equivalent noise current, obtained from the measured phase noise and resonator responsivity, is $\sim 80\text{pA}/\sqrt {\text{Hz}} $ with the strong-coupling channel.

The High Sensitivity Terahertz Detection Module (HSTDM), a key component of the backend modules on board the Chinese Space Station Survey Telescope (CSST), will offer great opportunities for the discovery of terahertz astronomy, with implications that extend well beyond China to the global astronomical community. It is imperative that the raw data collected by HSTDM undergo meticulous calibration and processing through the HSTDM data processing pipeline (HSTDM pipeline for short) to ensure the accuracy and effectiveness of the final science data to be archived for further research. This process necessitates that the HSTDM pipeline address instrumental artifacts and effects as well as the coordination of data flow of the scheduled observing sequences under all observing modes of HSTDM within the CSST automated processing environment. As the understanding of CSST HSTDM data processing develops during the pipeline development stage, it becomes essential to assess the accuracy, robustness and performance of the HSTDM pipeline under all observing modes of HSTDM so that components of the HSTDM pipeline be rationally added, removed, amended or extended within the modular framework. In this paper, we develop practical simulation methods to facilitate this need. The contribution of synthetic data generation of HSTDM observation includes two parts: (1) HSTDM instrumental effect simulation based on both real testing profiles and simulated models; (2) Observing data flow generation based on HSTDM observing mode scenario. The simulation methods have been implemented and shown to be practical in testing the HSTDM pipeline during the development stage.

Terahertz (THz) spectroscopy holds significant importance owing to the abundance of molecular and atomic fingerprint lines within this frequency range, enabling impactful applications in materials science, biology, and astronomy. Building on recent advancements in metasurface technology, we have developed a THz spectrometer that integrates a phase grating with two transmissive metasurfaces on a single platform. By mitigating chromatic dispersion and angular response limitations, the system incorporates a parallel focusing plane, simplifying integration with detector arrays, enhancing robustness, and reducing the requirement for incident light. Operating within the 1.23–1.43 THz range, the spectrometer achieves a theoretical resolution of 21 GHz, with a frequency resolution of 63 (f/Δf). This compact terahertz spectrometer offers scalable solutions for hyperspectral imaging and THz astronomical observation, demonstrating the transformative potential of metasurface technology for miniaturizing high-performance THz spectroscopy systems.

Transition-edge sensors (TESs) are among the most promising technologies for single-photon detection, offering high quantum efficiency, low dark count rates, and energy-resolving capabilities. However, optimal TES performance typically requires ultra-low temperatures below 100 mK, necessitating bulky dilution refrigerators or adiabatic demagnetization refrigerators, which limits their practical deployment. In this work, we demonstrate a titanium-based TES optimized for 1064 nm photon detection that achieves high performance at an elevated bath temperature of 220 mK—approximately 90% of its superconducting transition temperature, making it compatible with more compact sorption refrigerators. Through the integration of an optical cavity, a detailed complex impedance and noise characterization, and a systematic investigation of dark count sources, the detector achieves a system detection efficiency exceeding 97%, an energy resolution of 240 meV, and an intrinsic dark count rate as low as 2 × 10−4 cps. These findings significantly expand the applicability of TES single-photon detectors to practical photon-counting systems, such as quantum information and infrared astronomy.

The High Sensitivity Terahertz Detection Module (HSTDM), a key component of the backend modules on board the China Space Station Telescope (CSST), will offer great opportunities for the discovery of Terahertz Astronomy, with implications that extend well beyond China to the global astronomical community. It is imperative that the raw data collected by HSTDM undergoes meticulous calibration and processing through the HSTDM data processing pipeline (HSTDM pipeline for short) to ensure the accuracy and effectiveness of the final science data to be archived for further research. This process necessitates that the HSTDM pipeline address instrumental artifacts and effects as well as the coordination of data flow of the scheduled observing sequences under all observing modes of HSTDM within the CSST automated processing environment. As the understanding of CSST HSTDM data processing develops during the pipeline development stage, it becomes essential to assess the accuracy, the robustness and the performance of the HSTDM pipeline under all observing modes of HSTDM so that components of the HSTDM pipeline be rationally added, removed, amended or extended within the modular framework. In this paper, we develop practical simulation methods to facilitate this need. The contribution of synthetic data generation of HSTDM observation includes two parts: 1. HSTDM instrumental effect simulation based on both real testing profiles and simulated models; 2. Observing data flow generation based on HSTDM observing mode scenario. The simulation methods have been implemented and shown to be practical in testing the HSTDM pipeline during the development stage.

With moderate cooling requirements, YBCO-based superconducting detectors are promising for space applications from microwave to the terahertz regime. Their sensitivities, however, are still rather limited. The dielectric loss of the substrate on which YBCO films are deposited might play an important role in the detector performance. This study systematically characterizes the dielectric properties of three common commercially available substrates for YBCO film, i.e., Sapphire (Al₂O₃), Lanthanum aluminate (LaAlO₃), and Magnesium oxide (MgO), from 0.22 to 3 THz at 300, 77, and 20 K. It has been found that both Al₂O₃ and MgO substrates exhibit significantly reduced loss tangents (tanδ < 1×10^-5) at cryogenic temperatures (77 and 20 K), whereas LaAlO₃ maintains high dielectric loss tangents (tanδ > 3×10^-3) across all measured temperatures and frequencies.