Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

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.


  1. 1.

    Madau, P. & Dickinson, M. Cosmic star-formation history. Annu. Rev. Astron. Astr. 52, 415–486 (2014).

    ADS  Article  Google Scholar 

  2. 2.

    Nakagawa, T. et al. The next-generation infrared astronomy mission SPICA under the new framework. Proc. SPIE 9143, 91431I (2014).

    Article  Google Scholar 

  3. 3.

    Bradford, C. M. et al. A cryogenic space telescope for far-infrared astrophysics: a vision for NASA in the 2020 decade. Preprint at (2015).

  4. 4.

    Shaw, M. D., Bueno, J., Day, P. K., Bradford, C. M. & Echternach, P. M. Quantum capacitance detector: a pair-breaking radiation detector based on the single Cooper-pair box. Phys. Rev. B 79, 144511 (2009).

    ADS  Article  Google Scholar 

  5. 5.

    Bueno, J., Shaw, M. D., Day, P. K. & Echternach, P. M. Proof of concept of the quantum capacitance detector. Appl. Phys. Lett. 96, 103503 (2010).

    ADS  Article  Google Scholar 

  6. 6.

    Bueno, J., Llombart, N., Day, P. K. & Echternach, P. M. Optical characterization of the quantum capacitance detector at 200 μm. Appl. Phys. Lett. 99, 173503 (2011).

    ADS  Article  Google Scholar 

  7. 7.

    Stone, K. J. et al. Real time quasiparticle tunneling measurements on an illuminated quantum capacitance detector. Appl. Phys. Lett. 100, 263509 (2012).

    ADS  Article  Google Scholar 

  8. 8.

    Echternach, P. M. et al. Photon shot noise limited detection of terahertz radiation using a quantum capacitance detector. Appl. Phys. Lett. 103, 053510 (2013).

    ADS  Article  Google Scholar 

  9. 9.

    Wilson, C. M. & Prober, D. E. Quasiparticle number fluctuations in superconductors. Phys. Rev. B 69, 094524 (2004).

    ADS  Article  Google Scholar 

  10. 10.

    Kozorezov, A. G. et al. Quasiparticle-phonon downconversion in nonequilibrium superconductors. Phys. Rev. B 61, 11807–11819 (2000).

    ADS  Article  Google Scholar 

  11. 11.

    Wang, C. et al. Measurement and control of quasiparticle dynamics in a superconducting qubit. Nat. Commun. 5, 5836 (2014).

    Article  Google Scholar 

  12. 12.

    Day, P. K., LeDuc, H. G., Mazin, B. A., Vayonakis, A. & Zmuidzinas, J. Broadband superconducting detector suitable for use in large arrays. Nature 425, 817–821 (2003).

    ADS  Article  Google Scholar 

  13. 13.

    De Visser, P. J., Baselmans, J. J. A., Bueno, J., Llombart, N. & Klapwijk, T. M. Fluctuations in the electron system of a superconductor exposed to a photon flux. Nat. Commun. 5, 3130 (2014).

    Article  Google Scholar 

  14. 14.

    De Visser, P. J. et al. Number fluctuations of sparse quasiparticles in a superconductor. Phys. Rev. Lett. 106, 167004 (2011).

    ADS  Article  Google Scholar 

  15. 15.

    Machlup, S. Noise in semiconductors: spectrum of a two-parameter random signal. J. Appl. Phys. 25, 341–343 (1954).

    ADS  Article  MATH  Google Scholar 

  16. 16.

    Guillaume, A., Schneiderman, J. F., Delsing, P., Bozler, H. M. & Echternach, P. M. Free evolution of superposition states in a single Cooper pair box. Phys. Rev. B 69, 132504 (2004).

    ADS  Article  Google Scholar 

  17. 17.

    Persky, M. J. Review of black surfaces for space-borne infrared systems. Rev. Sci. Instrum. 70, 2193–2217 (1999).

    ADS  Article  Google Scholar 

  18. 18.

    Benford, D. J., Gaidis, M. C. & Kooi, J. W. Optical properties of Zitex in the infrared to submillimeter. Appl. Opt. 42, 5118–5122 (2003).

    ADS  Article  Google Scholar 

Download references


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.

Corresponding author

Correspondence to P. M. Echternach.

Ethics declarations

Competing interests

The authors declare no competing financial interests

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Electronic supplementary material

Supplementary Information

Supplementary Figure 1, Supplementary Table 1, Supplementary Text and Supplementary References

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing