Abstract— This paper summarizes our receiver noise temperature data of NbN HEB mixers obtained at a number of local oscillator frequencies between 1.9 to 4.3 THz in order to verify the role of quantum noise. The experimental data show that the receiver noise temperature increases roughly linearly with frequency. At 4.3 THz, we measured a receiver noise temperature of 1300 K, which is about 6 times (hf/k_B). The noise data at different frequencies are compared to a prediction of a noise model including the contribution of quantum noise and making use of a hot-spot model for mixing.  We draw a preliminary conclusion that at 4.3 THz roughly 30% of the total receiver noise temperature can be ascribed to the quantum noise. However, more dedicated measurements are required in order to further support the quantum noise model for HEB mixers.

Index Terms—heterodyne receiver, superconducting hot electron bolometer mixer, THz mixer, terahertz, quantum noise

Manuscript received 19 August 2008. P. Khosropanah is with SRON Netherlands Institute for Space Research Landleven 12, 9747 AD Groningen, The Netherlands. (Corresponding author is P. Khosropanah, phone: +31-50-363-3465, fax: +31-50-363-4033, e-mail: P.Khosropanah@sron.nl).
W. Zhang is with Purple Mountain Observatory (PMO), Chinese Academy of Sciences, 2 West Beijing Road, Nanjing, JiangSu 210008, China, and is also with SRON Netherlands Institute for Space Research Landleven 12, 9747 AD Groningen, The Netherlands.
E. L. Kollberg is with the Department of Microelectronics and Nano Science, Chalmers University of Technology, SE-41296 Göteborg, Sweden
K. S. Yngvesson is with the Department of Electrical and Computer Engineering, University of Massachusetts, Amherst MA 01003 USA.
J.R. Gao, T. Bansal and. M. Hajenius are with SRON Netherlands Institute for Space Research, Utrecht/Groningen, the Netherlands and are also with Kavli Institute of NanoScience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, the Netherlands.

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