Our Universe is most radiant at terahertz frequencies (0.1–10.0 THz) (ref. 1), providing critical information on the formation of the planets, stars and galaxies, as well as the atmospheric constituents of the planets, their moons, comets and asteroids2,3,4,5,6,7,8,9. The detection of faint fluxes of photons at terahertz frequencies is crucial for many planetary, cosmological and astrophysical studies10,11,12,13,14. For example, understanding the physics and molecular chemistry of the life cycle of stars and their relationship with the interstellar medium in galaxies requires heterodyne detectors with noise temperatures close to the quantum limit15. Near-quantum-limited heterodyne terahertz detection has so far been possible only through the use of cryogenically cooled superconducting mixers as frequency downconverters15,16,17,18. Here we introduce a heterodyne terahertz detection scheme that uses plasmonic photomixing for frequency downconversion to offer quantum-level sensitivities at room temperature. Frequency downconversion is achieved by mixing terahertz radiation and a heterodyning optical beam with a terahertz beat frequency in a plasmonics-enhanced semiconductor active region. We demonstrate terahertz detection sensitivities down to three times the quantum limit at room temperature. With a versatile design capable of broadband operation over a 0.1–5.0 THz bandwidth, this plasmonic photomixer has broad applicability to astronomy, cosmology, atmospheric studies, gas sensing and quantum optics.
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The authors declare that all data supporting the conclusions of the manuscript are present in the manuscript and the supplementary materials.
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We gratefully acknowledge financial support from National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) Strategic University Research Partnerships Program. M.J.’s group gratefully acknowledges the financial support from the Office of Naval Research (contract number N00014-14-1-0573) and National Science Foundation (contract number 1305931). S.C. was supported by the Department of Energy (grant number DE-SC0016925).
The authors declare no competing interests.
Peer review information: Nature Astronomy thanks Heinz-William Huebers, Juerg Leuthold and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Figs. 1–6, Supplementary Table 1