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arXiv:2305.14643 · IEEE Transactions on Applied Superconductivity

Terahertz Imaging System With On-Chip Superconducting Josephson Plasma Emitters for Nondestructive Testing

Manabu Tsujimoto, Kaveh Delfanazari, Takanari Kashiwagi, Toshiaki Hattori, Kazuo Kadowaki

Published Mar 17, 2026• 2 citations
arXivHTMLPDF

Abstract

Compared with neighboring microwave and infrared bands, terahertz (THz) frequencies offer unique advantages for imaging applications. In particular, characteristic THz spectral fingerprints of chemicals enable nondestructive evaluation and imaging of biological objects, materials, components, electronic circuits, and systems, with broad relevance to security, medical diagnostics, materials science, pharmaceutical inspection, aeronautics, and electronics industries. Despite this potential, practical THz imaging systems have been limited by the scarcity of compact, power-efficient, and tunable THz sources. In this work, we employ high-temperature superconducting monolithic sources—Josephson plasma emitters (JPEs)—as chip integrated, coherent, monochromatic, and broadly tunable THz wave emitters, and demonstrate nondestructive THz imaging of concealed metallic surgical blades, floppy disks, dandelion leaves, and sliced pork meat. The resulting images exhibit high contrast between metallic and non-metallic regions, reveal fine structural features of diverse objects, and enable selective visualization of different powdered materials. These results establish the feasibility of a compact THz imaging system based on on-chip superconducting sources for nondestructive, contactless, rapid, and accurate applications in environmental monitoring, security screening, medical diagnostics, materials characterization, and quantum science and technology.

DOI
10.1109/tasc.2026.3674700

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Compared with neighboring microwave and infrared bands, terahertz (THz) frequencies offer unique advantages for imaging applications. In particular, characteristic THz spectral fingerprints of chemicals enable nondestructive evaluation and imaging of biological objects, materials, components, electronic circuits, and systems, with broad relevance to security, medical diagnostics, materials science, pharmaceutical inspection, aeronautics, and electronics industries. Despite this potential, practical THz imaging systems have been limited by the scarcity of compact, power-efficient, and tunable THz sources. In this work, we employ high-temperature superconducting monolithic sources—Josephson plasma emitters (JPEs)—as chip integrated, coherent, monochromatic, and broadly tunable THz wave emitters, and demonstrate nondestructive THz imaging of concealed metallic surgical blades, floppy disks, dandelion leaves, and sliced pork meat. The resulting images exhibit high contrast between metallic and non-metallic regions, reveal fine structural features of diverse objects, and enable selective visualization of different powdered materials. These results establish the feasibility of a compact THz imaging system based on on-chip superconducting sources for nondestructive, contactless, rapid, and accurate applications in environmental monitoring, security screening, medical diagnostics, materials characterization, and quantum science and technology.
Abstract Terahertz (THz) technology is a rapidly developing field that explores the use of electromagnetic waves in the THz frequency range. The unique properties of THz waves have great application prospects in electromagnetic sensing, security inspection, non-destructive testing, medical diagnostics, biology, high-speed wireless communication, space science and so on. At present, the application of THz technology is still under continuous research and development, and its broad scientific prospects are recognized worldwide. THz frequency falls into the gap on the electromagnetic spectrum of electronics and optics, thus both classic microwave and optical technologies cannot be directly applied to the THz systems. New components, circuits and application systems are being developed for THz technology. Superconductivity is a quantum mechanical phenomenon and offers unique advantages for applications in high-frequency electromagnetic domains. Novel superconducting quantum devices are being exploited for THz wave radiation and detection, and many THz application systems. The high-T c superconducting (HTS) electronic devices have great potential in emerging THz technologies due to its very high-energy bandgap (well into THz regions) and much relaxed cooling requirement, and they offer strong prospect for the development of practical and portable THz systems. This paper provides an overview of the state-of-art development of HTS THz quantum devices and their application for THz sensing, imaging and communication. The review will start with a brief introduction about cutting-edge THz technology, the fundamental of superconductivity, Josephson effects and the HTS Josephson junctions. Then, the research progress and the latest achievement of HTS Josephson THz emitters, detectors and mixers will be reviewed, followed by their application examples in some THz systems. Finally, the conclusion, challenges and outlooks of the HTS technologies in THz applications are discussed.
Despite its potential for e.g.e.g.e.g. medical imaging, wireless communication, and ultrasensitive analysis of biological materials, the terahertz frequency range of light cannot be suitably utilized without practical solid-state sources. A naturally formed stack of superconducting junctions emits terahertz radiation, owing to synchronization of macroscopic wave functions, and the authors propose a means to manipulate that synchronization, which is the most promising way to attain a versatile superconducting terahertz source. Their findings also give insight into the quantum physics of entangled photons emitted from superconductors.
The CSIRO Applied Superconductivity Group has a long-term effort in research and development of superconducting electronic devices and systems for various practical applications. In this paper, I will mainly describe our recent research progress in developing novel HTS Josephson devices for high frequency applications. Specifically, we have recently developed a novel HTS Josephson heterodyne gigahertz (GHz) microwave oscillator and on-chip down-converter (mixer). For even higher frequency application, we developed a HTS Josephson junction terahertz (THz) detector and applied it successfully to THz imaging. I will highlight some of the recent results and describe the on-going effort of developing an array of such detectors and associated electronics as well as system integration.
Terahertz imaging has become increasingly important across various fields and practical production applications. Achieving both high sensitivity and high speed remains a primary challenge for most current THz imaging technologies. In this work, we present an imaging system based on Rydberg atomic vapor operating at frequencies exceeding 1 THz. By utilizing Cesium 133 atoms coupled with THz waves, de-excitation radiation generated after atomic excitation to Rydberg states converts invisible THz waves into visible light, enabling the acquisition of spatial information and intensity distributions of THz fields. The system achieves a minimum detectable power of 330 fW /s 1/2 per (2.4×2.4) μm 2 , an imaging resolution of approximately 1.7 mm, and an imaging bandwidth of 8.6 MHz. Additionally, the theoretical imaging rate can exceed 1 MHz. The Rydberg-atom-based THz imaging system exhibits a simple structure and is amenable to miniaturization. This THz imaging method holds promise for advancing applications in THz nondestructive testing, biomedical imaging, and concealed object detection.
The terahertz regime, as a last radio window, remains to be fully explored, and astronomical and atmospheric observations in this regime are scientifically important. Like other frequency regimes, developing high-sensitivity detectors (coherent and incoherent) is of particular significance for both ground-based and space-borne facilities. As the coherent detector of choice below 1.4 THz, superconductor-insulator-superconductor (SIS) heterodyne mixers have achieved as high a sensitivity as five times the quantum limit around 1.4 THz. It is, however, still a challenge to developing SIS mixers at frequencies beyond 1.4 THz with considerable transmission loss in superconducting circuits due to the Cooper-pair breaking by energetic photons and increased many difficulties in designing and fabricating. So far, superconducting hot electron bolometer (HEB) mixers have been the most sensitive heterodyne detectors at frequencies above 1.5 THz, and successfully used to detect molecular spectral lines up to 2.5 THz from ground-based and space telescopes. Although spiral-antenna coupled NbN HEB mixers show a good sensitivity in the whole THz frequency range, the directly measured spectral response with Fourier transform spectrometer falls quickly as frequency increases, especially above 3 THz. The terahertz band is also of particular importance to observe astronomical objects such as cosmic microwave background, early distant objects, cold objects and dusty objects. Aiming at such objects, we develop a terahertz imaging array system by combining advanced superconducting detectors such as transition edge sensor (TES) and microwave kinetic inductance detectors (MKIDs), thus the system has a frequency band centred at 350 m, an operational temperature of 0.3 K, and a sensitivity reaching background limit performance for ground-based applications. In addition, it is expected to have some breakthroughs in ultra-sensitive superconducting TES and MKID, low noise multi-channel readout and multiplexing, efficient terahertz-wave coupling technology, and large-scale array system integration. The developed terahertz imaging array system will serve as the next-generation instrument of Dome A 5 m terahertz telescope, conducting a 350 m-band legacy survey for studying the planets, stars, galaxies and cosmology. Besides the application in astronomy, the developed terahertz imaging array system can also be applied to some areas requiring rapid detection such as security, deep space exploration, and biomedical imaging. In this paper, we mainly introduce the superconducting detectors developed at Purple Mountain Observatory and those for international collaborative projects.
Correlating superconducting qubit performance with advanced materials analysis is a key strategy for improving coherence. Existing diagnostics for key properties, such as dielectric loss, structural discontinuity, and interface heterogeneity, often rely on destructive electron microscopy or low-throughput millikelvin measurements. Here, we demonstrate noninvasive terahertz (THz) nano-imaging/spectroscopy of encapsulated niobium transmon qubits as a high-throughput proxy for performance evaluation. We identify large variations in sidewall near-field signals, implicating sidewall loss and discontinuity as major coherence limiters, and also use THz hyperspectral line scans to probe dielectric responses and field participation at Al junction interfaces.