The role of quantum noise in terahertz receivers

We have revised and considerably extended our paper on quantum noise at the 13 th ISSTT. In the present paper we first review general quantum mechanical limits on the sensitivity of heterodyne receivers. We introduce the ideal broad band mixer (IBBM), which has a receiver noise temperature of zero Kelvin. Based on the hot-spot model of a real HEB mixer, we model it as an IBBM in series with a passive resistance. An expression for the HEB receiver noise temperature, including optical input loss is then derived. We find that the predicted DSB receiver noise temperature agrees well with three sets of measured data. The result suggests that quantum noise and classical HEB noise contribute about equally at low terahertz frequencies while at higher terahertz frequencies quantum noise dominates.