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\bibitem{Gao_etal2007} Gao, J. R., Hajenius, M., Yang, Z. Q., Baselmans, J. J. A., Khosropanah, P., Barends, R., et al. (2007). Terahertz superconducting hot electron bolometer heterodyne receivers. \textit{IEEE Trans. Appl. Supercond.}, \textit{17}(2), 252--258.

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