Single photon detection of 1.5 THz radiation with the quantum capacitance detector


Far-infrared spectroscopy can reveal secrets of galaxy evolution and heavy-element enrichment throughout cosmic time, prompting astronomers worldwide to design cryogenic space telescopes for far-infrared spectroscopy. The most challenging aspect is a far-infrared detector that is both exquisitely sensitive (limited by the zodiacal-light noise in a narrow wavelength band, λ/Δλ ~1,000) and array-able to tens of thousands of pixels. We present the quantum capacitance detector, a superconducting device adapted from quantum computing applications in which photon-produced free electrons in a superconductor tunnel into a small capacitive island embedded in a resonant circuit. The quantum capacitance detector has an optically measured noise equivalent power below 10−20 W Hz−1/2 at 1.5 THz, making it the most sensitive far-infrared detector ever demonstrated. We further demonstrate individual far-infrared photon counting, confirming the excellent sensitivity and suitability for cryogenic space astrophysics.

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Fig. 1: QCD concept.
Fig. 2: Measurement schematics, experimental setup and device.
Fig. 3: Device response and NEP.
Fig. 4: Quasiparticle tunnelling measurements.
Fig. 5: Single photon measurements.
Fig. 6: Photon statistics and counting.


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We thank R. E. Muller for performing the electron beam lithography and D. W. Wilson for the design and fabrication of the Fresnel lens array. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. US Government sponsorship acknowledged.

Author information

P.M.E designed and fabricated the devices, performed the experiments, analysed the data and wrote the paper. C.M.B. devised the experiment goals and some experiment protocols. T.R. performed simulations of the interaction of radiation with the devices. B.J.P. contributed to the data analysis and the calculation of the radiation incident on the devices. All authors contributed to preparing the paper.

Correspondence to P. M. Echternach.

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Echternach, P.M., Pepper, B.J., Reck, T. et al. Single photon detection of 1.5 THz radiation with the quantum capacitance detector. Nat Astron 2, 90–97 (2018).

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