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arXiv:2003.05966 · Physical Review Applied

Hypersensitive Tunable Josephson Escape Sensor for Gigahertz Astronomy

Federico Paolucci, Nadia Ligato, Vittorio Buccheri, Gaia Germanese, Pauli Virtanen, Francesco Giazotto

Published Sep 21, 2020• 11 citations
arXivHTMLPDF

Abstract

In astrophysics and particle physics, interest is shifting from the TeV scale toward $\ensuremath{\mu}$eV phenomena, such as the cosmic microwave background, galaxy formation, and the search for dark matter. To this end, superconducting detectors are employed. This study exploits modulation of the escape temperature via current to demonstrate a Josephson escape sensor (JES). The JES promises a stunning noise-equivalent power of ${10}^{\ensuremath{-}25}$ W/Hz${}^{1/2}$, and the possibility to detect single photons down to 2 GHz in frequency. This device could also have strong implications in quantum technology, from subterahertz communication and quantum computing to cryptography and quantum key distribution.

DOI
10.1103/physrevapplied.14.034055

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In astrophysics and particle physics, interest is shifting from the TeV scale toward \ensuremathμ\ensuremath{\mu}\ensuremathμeV phenomena, such as the cosmic microwave background, galaxy formation, and the search for dark matter. To this end, superconducting detectors are employed. This study exploits modulation of the escape temperature via current to demonstrate a Josephson escape sensor (JES). The JES promises a stunning noise-equivalent power of 10\ensuremath−25{10}^{\ensuremath{-}25}10\ensuremath−25 W/Hz1/2{}^{1/2}1/2, and the possibility to detect single photons down to 2 GHz in frequency. This device could also have strong implications in quantum technology, from subterahertz communication and quantum computing to cryptography and quantum key distribution.
The origin and the evolution of the universe are concealed in the evanescent diffuse extragalactic background radiation (DEBRA). To reveal these signals, the development of innovative ultra-sensitive bolometers operating in the gigahertz band is required. Here, we review the design and experimental realization of two bias-current-tunable sensors based on one dimensional fully superconducting Josephson junctions: the nanoscale transition edge sensor (nano-TES) and the Josephson escape sensor (JES). In particular, we cover the theoretical basis of the sensors operation, the device fabrication, their experimental electronic and thermal characterization and the deduced detection performance. Indeed, the nano-TES promises a state-of-the-art noise equivalent power (NEP) of about 5×10−20 W/Hz, while the JES active region is expected to show an unprecedented NEP of the order of 10−25 W/Hz. Therefore, the nano-TES and JES are strong candidates to push radio astronomy to the next level.
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The detection of single microwave photons is becoming a cornerstone of fundamental experiments in circuit quantum electrodynamics and quantum sensing. Experiments in cavity quantum electrodynamics, photon-mediated entanglement, dark-matter axion searches and quantum thermodynamics increasingly rely on single-photon sensitivity. Current technologies exploit superconducting devices, including Josephson parametric detectors, and transmon-based non-demolition counters for dark-matter haloscopes. Hybrid double quantum dot-Josephson systems reach interesting levels of efficiency, while current-biased Josephson junctions show potential for near-quantumlimited resolution. Despite impressive progress, challenges remain in reducing dark counts, improving reset speed, and scaling for multiplexed arrays. Continued advances in superconducting materials, qubit coherence, and hybrid semiconductor-superconductor designs promise to extend detection efficiency and bandwidth. These developments are poised to enable the next generation of quantum-enabled experiments, from foundational tests in quantum optics to searches for new physics.
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Graphene Josephson junctions (JJ) provide a promising platform for ultra-broadband quantum sensing of light owing to graphene's frequency-independent absorption, vanishing electronic heat capacity, and weak electron-phonon coupling, which enable rapid suppression of the critical current through radiation-induced electron heating. Existing investigations have been confined to the microwave and infrared regimes, where competing detector technologies are already established; by contrast, the terahertz (THz) band - where sensitivity is most urgently lacking and no mature quantum sensor exists - has remained largerly unexplored. Here we demonstrate a strong photoresponse of graphene JJs at THz frequencies, establishing a first experimental step towards graphene-based THz quantum sensors. Under low-intensity illumination, we observe a pronounced suppression of the critical current that generates a strong photovoltage (Vph) under current bias. By tracking this Vph and independently measuring the electron temperature as a function of absorbed power, we extract a responsivity of 88 kV W^-1 and a noise-equivalent power of 45 aW Hz^-1/2 at 1.7 K. Furthermore, gate tunability of our JJ enables access to a regime where hysteretic current-voltage characteristics persist up to 0.9 K, offering a potential route toward single-photon THz detection beyond millikelvin (mK) temperatures. These findings establish graphene JJ as a versatile platform for broadband cryogenic radiation sensing and point towards their use as quantum sensors at THz frequencies.
Detection of light dark matter, such as axion-like particles, puts stringent requirements on the efficiency and dark-count rates of microwave-photon detectors. The possibility of operating a current-biased Josephson junction as a single-microwave photon-detector was investigated through numerical simulations, and through an initial characterization of two Al junctions fabricated by shadow mask evaporation, done in a dilution refrigerator by measuring escape currents at different temperatures, from 40 mK up to the Al transition temperature. The escape dynamics of the junctions were reproduced in the simulation, including the dissipative effects. Inhibition of thermal activation was observed, leaving the macroscopic quantum tunneling as the dominant effect well beyond the crossover temperature.