Large gain, negative resistance, and oscillations in superconducting quasiparticle heterodyne mixers

Abstract

We have measured the properties of a superconductor-insulator-superconductor quasiparticle mixer which is operated in the quantum limit. Single sideband conversion gain larger than +4 dB was observed at 36 GHz with a mixer noise temperature T = 9±6 K, which is to be compared with the (Planck) quantum limit h/ω/(k ln 2)≃2.5 K. Complete three-port mixer calculations are presented which are in good agreement with the gain measurements. The dynamic resistance was observed to become infinite and then negative as the source conductance was decreased. This implies that arbitrarily large gain is available. The negative resistance is accompanied by IF oscillations.

Quantum detection at millimeter wavelengths

“…The mixer thus acts as a constant-current source at the IF when GL =0 (this is also clear from Fig. ll), and the available output power will scale with the dynamic resistance RD --(GL ) '. This important aspect of SIS mixer performance was first appreciated by McGrath et al (1981), and results of their mixing experiments performed on Sn junctions similar to the one shown in Fig. 13 are illustrated in Figs.…”

“…Negative resistance and a net conversion efficiency greater than unity were reported by Smith, McGrath, Richards, van Kempen, Prober, and Santhanam (1981) at 36 GHz; and in collaboration with Batchelor (McGrath et al , 1981) they obtained a large conversion gain I. '&4 dB together with a mixer noise temperature TM -9 K (Sficolk near the quantum limit.…”

“…In both cases this demonstration was marginal: both found a SSB conversion slightly better than 3-dB loss, implying a slight gain for doublesideband operation. The quantum theory prediction was more firmly established when McGrath et al (1981;see also Smith et al , 1981b) and Kerr et al (1981) reported infinite available conversion gain at 36 and 115 GHz, respectively. This meant that arbitrarily high small-signal gain could be achieved with an appropriately matched IF load.…”

A Very Low Noise Quasiparticle (SIS) Mixer Receiver for Radio Astronomical Applications

“…Since 1979 it has been evident that a superconducting quasiparticle mixer is an attractive alternative, which may offer almost as low noise temperatures as the maser but a larger flexibility concerning bandwidth and tunability. It will noisewise be superior to the cooled Schottky-barrier diode mixer and can certainly be operated from 10 GHz up to several hundred GHz [2][3][4][5][6].…”

“…3 curve (a)). The differential resistance dv/di switches from a high to a low value at: (a) quite low currents causing a very low shot noise, and (b) within a voltage interval Av " hf/e, causing quantum effects in the mixing process which can be used to produce conversion gain [3,6).…”