Spectacular advances in heterodyne astronomy1,2 have been largely due to breakthroughs in detector technology3. To exploit the full capacity of future terahertz (∼300 GHz–5 THz) telescope space missions4, new concepts of terahertz coherent receivers are needed, providing larger bandwidths and imaging capabilities with multipixel focal plane heterodyne arrays5. Here we show that graphene uniformly doped to the Dirac point, with material resistance dominated by quantum localization and thermal relaxation governed by electron diffusion, enables highly sensitive and wideband coherent detection of signals from 90 to 700 GHz and, prospectively, across the entire terahertz range. We measure on proof-of-concept graphene bolometric mixers an electron diffusion-limited gain bandwidth of 8 GHz (corresponding to a Doppler shift of 480 km s−1 at 5 THz) and intrinsic mixer noise temperature of 475 K (which would be equivalent to ~2 hf/kB at f = 5 THz, where h is Planck’s constant, f is the frequency and kB is the Boltzmann constant), limited by the residual thermal background in our setup. An optimized device will result in a mixer noise temperature as low as 36 K, with the gain bandwidth exceeding 20 GHz, and a local oscillator power of <100 pW. In conjunction with the emerging quantum-limited amplifiers at the intermediate frequency6,7, our approach promises quantum-limited sensing in the terahertz domain, potentially surpassing superconducting technologies, particularly for large heterodyne arrays.
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The authors declare that the main data supporting the findings of this study are available within the article and its Supplementary Information files. Additional data is available from the corresponding author upon request.
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We thank J. Conway and E. De Beck for illuminating discussions, and A. Tzalenchuk, J. F. Schneiderman and T. Claeson for critical reading of the manuscript. This work was jointly supported by the Swedish Foundation for Strategic Research (SSF) (nos. IS14-0053, GMT14-0077, RMA15-0024), Knut and Alice Wallenberg Foundation, Chalmers Area of Advance NANO, the Swedish Research Council (VR) 2015-03758 and 2016-04828, the Swedish-Korean Basic Research Cooperative Program of the NRF (no. NRF-2017R1A2A1A18070721) and the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 766714/HiTIMe).
The authors declare no competing interests.
Peer review information Nature Astronomy thanks Peter Roelfsema and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Lara-Avila, S., Danilov, A., Golubev, D. et al. Towards quantum-limited coherent detection of terahertz waves in charge-neutral graphene. Nat Astron 3, 983–988 (2019). https://doi.org/10.1038/s41550-019-0843-7
IEEE Transactions on Terahertz Science and Technology (2019)