Towards quantum-limited coherent detection of terahertz waves in charge-neutral graphene

TL;DR

This paper demonstrates that charge-neutral graphene can be used to develop highly sensitive, wideband coherent detectors for terahertz waves, potentially enabling quantum-limited sensing and large array applications in future space telescopes.

Contribution

It introduces a novel graphene-based coherent detection method for THz signals with wide bandwidth and high sensitivity, surpassing existing superconducting technologies.

Findings

Achieved an 8 GHz gain bandwidth in graphene bolometers.

Demonstrated a mixer noise temperature of 475 K.

Projected improvements could lower noise temperature to 36 K with >20 GHz bandwidth.

Abstract

Spectacular advances in heterodyne astronomy with both the Herschel Space Observatory and Stratospheric Observatory for Far Infrared Astronomy (SOFIA) have been largely due to breakthroughs in detector technology. In order to exploit the full capacity of future THz telescope space missions (e.g. Origins Space Telescope), new concepts of THz coherent receivers are needed, providing larger bandwidths and imaging capabilities with multi-pixel focal plane heterodyne arrays. Here we show that graphene, uniformly doped to the Dirac point, enables highly sensitive and wideband coherent detection of THz signals. With material resistance dominated by quantum localization, and thermal relaxation governed by electron diffusion, proof-of-concept graphene bolometers demonstrate a gain bandwidth of 8 GHz and a mixer noise temperature of 475 K, limited by 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 lower than 100 pW. In conjunction with the emerging quantum-limited amplifiers at the intermediate frequency, our approach promises quantum-limited sensing in the THz domain, potentially surpassing superconducting technologies, particularly for large heterodyne arrays.