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arXiv:2409.16050 · Nature Communications

Cascade switching current detectors based on arrays of Josephson junctions

Roger Cattaneo, Artemii E. Efimov, Kirill I. Shiianov, Oliver Kieler, V. M. Krasnov

Published Aug 25, 2025• 4 citations
arXivHTMLPDF

Abstract

Abstract Cascade multiplication is widely used to enhance photon detector sensitivity. While vacuum tube and semiconductor photomultipliers achieve high gains in the optical range, their performance at lower frequencies is limited by large work functions. Superconducting detectors overcome this constraint, enabling operation in the terahertz (THz) and microwave (MW) ranges. Here we introduce a concept of cascade-amplified superconducting detectors based on Josephson junction arrays. Interjunction coupling in an array triggers avalanche-like switching of multiple junctions upon photon absorption, resulting in cascade amplification of the readout voltage and an increased signal-to-noise ratio. We present prototypes using either low-T c linear Nb/NbxSi1−x/Nb arrays or Bi2Sr2CaCu2O8+δ high-T c stacked intrinsic Josephson junctions. Both MW and THz responses are analyzed and the advantages of the cascade detector over a conventional single-junction detector are demonstrated. Our findings suggest that Josephson junction arrays hold promise for the development of highly sensitive, broadband MW-to-THz detectors.

DOI
10.1038/s41467-025-63360-y

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Abstract Cascade multiplication is widely used to enhance photon detector sensitivity. While vacuum tube and semiconductor photomultipliers achieve high gains in the optical range, their performance at lower frequencies is limited by large work functions. Superconducting detectors overcome this constraint, enabling operation in the terahertz (THz) and microwave (MW) ranges. Here we introduce a concept of cascade-amplified superconducting detectors based on Josephson junction arrays. Interjunction coupling in an array triggers avalanche-like switching of multiple junctions upon photon absorption, resulting in cascade amplification of the readout voltage and an increased signal-to-noise ratio. We present prototypes using either low-T c linear Nb/NbxSi1−x/Nb arrays or Bi2Sr2CaCu2O8+δ high-T c stacked intrinsic Josephson junctions. Both MW and THz responses are analyzed and the advantages of the cascade detector over a conventional single-junction detector are demonstrated. Our findings suggest that Josephson junction arrays hold promise for the development of highly sensitive, broadband MW-to-THz detectors.
Current-biased Josephson junctions can act as detectors of electromagnetic radiation. At optimal conditions, their sensitivity is limited by fluctuations causing stochastic switching from the superconducting to the resistive state. This work provides a quantitative description of a stochastic switching current detector, based on an underdamped Josephson junction. It is shown that activation of a Josephson plasma resonance can greatly enhance the detector responsivity in proportion to the quality factor of the junction. The ways of tuning the detector for achieving optimal operation are discussed. For realistic parameters of Nb / Al O x / Nb tunnel junctions, the sensitivity and noise-equivalent power (NEP) can reach values of S ≃ 5 × 10 12 (V/W) and NEP ≃ 2 × 10 − 23 ( WHz − 1 / 2 ), respectively. These outstanding characteristics facilitate both bolometric and single-photon detection in microwave and terahertz ranges. Published by the American Physical Society 2024
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.
high-temperature superconductor represent stacks of atomic scale intrinsic Josephson junctions. They can be used for generation of high-frequency electromagnetic waves. Here we analyze Josephson emission from small-but-high mesas (with a small area, but containing many stacked junctions). We have found strong evidence for tunable terahertz emission with a good efficacy in a record high-frequency span 1-11 THz, approaching the theoretical upper limit for this superconductor. Emission maxima correspond to in-phase cavity modes in the mesas, indicating coherent superradiant nature of the emission. We conclude that terahertz emission requires a threshold number of junctions N ~ 100. The threshold behavior is not present in the classical description of stacked Josephson junctions and suggests importance of laser-like cascade amplification of the photon number in the cavity.
Sources of light in the terahertz (THz) wavelength range are extensively researched, and tunable planar Josephson junctions seem promising.They can be used e.g.e.g.e.g. to calibrate sensitive detectors, but not all of the energy poured into the junctions is converted to THz light. Knowing how many photons come out is not simply a matter of knowing how much energy went in. To address this problem, the authors employ a detector that discriminates between coherent THz radiation and thermally induced blackbody radiation, with single-photon sensitivity.
Single photon detectors (SPDs) at terahertz (THz) waveband are necessary for the THz applications. The superconducting quantum capacitance detectors (QCDs) are proved to be ultra-sensitive at THz waveband. 1.5 THz single photon detection has been achieved. Besides their sensitivity, large array of QCDs has also developed. Therefore, it is convenient of QCDs to achieve multiplexing through a microwave feedline like MKIDs. A QCD consists of a high quality factor (Q) microwave superconducting resonators and a single cooper-pair box (SCB). The microwave resonators are fabricated using tantalum (Ta) or niobium (Nb). The SCB is made of aluminum (Al). The ground electrode of the SCB is designed to be an absorber at THz waveband. The absorber is an inductive absorber consisting of orthogonal Al nanowires. Finally, we succeeded in measuring the periodic quantum capacitance signals. However, the responsivity is relatively low due to its weak coupling to the resonators of SCB. In the future, we need to optimize the performance of the detectors. QCDs are a prospect candidate of the next-generation astronomy observation and so on.
Superconducting tunnel junctions, which are also known as superconductor-insulator-superconductor (SIS) junctions, are widely used in coherent detection (heterodyne mixing) of electromagnetic radiation at millimeter and submillimeter wavelengths to achieve high spectral resolution (Δν/ν<10-6). With extremely low dark current and high quantum efficiency, superconducting tunnel junctions are also promising for THz photon detection. Besides the merit of high detection sensitivity, THz photon detectors with superconducting tunnel junctions can be operated at relatively high temperatures (above 0.3 K) and don't need rather complicated filtering systems by simply incorporating a superconducting resonant circuit with superconducting tunnel junctions. This paper mainly investigates the characteristics of THz photon detectors with Nb and NbN-based superconducting tunnel junctions. The MAR effect and associated shot noise are addressed. Some analytical and preliminary experimental results are presented.