Towards quantumlimited coherent detection of terahertz waves in chargeneutral graphene
Abstract
Spectacular advances in heterodyne astronomy^{1,2} have been largely due to breakthroughs in detector technology^{3}. To exploit the full capacity of future terahertz (∼300 GHz5 THz) telescope space missions^{4}, new concepts of terahertz coherent receivers are needed, providing larger bandwidths and imaging capabilities with multipixel focal plane heterodyne arrays^{5}. 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 proofofconcept graphene bolometric mixers an electron diffusionlimited 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/k_{B} at f = 5 THz, where h is Planck's constant, f is the frequency and k_{B} 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 quantumlimited amplifiers at the intermediate frequency^{6,7}, our approach promises quantumlimited sensing in the terahertz domain, potentially surpassing superconducting technologies, particularly for large heterodyne arrays.
 Publication:

Nature Astronomy
 Pub Date:
 August 2019
 DOI:
 10.1038/s4155001908437
 arXiv:
 arXiv:1904.03247
 Bibcode:
 2019NatAs...3..983L
 Keywords:

 Condensed Matter  Mesoscale and Nanoscale Physics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 15 pages, 4 figures