Conversion gain in mm-wave quasiparticle heterodyne mixers

Abstract

We report the observation of heterodyne mixing in superconductor-insulator-superconductor tunnel junctions with significant conversion gain and with a noise temperature comparable to the photon noise limit. (Double sideband L−1=1.400.14, TM≲1.5 K at 36 GHz.) The mixing arises from the strong nonlinearity in the quasiparticle tunneling currents at voltages comparable to the full energy gap. Gain is observed when the onset of quasiparticle current is sufficiently sharp that quantum effects are important. The observed gain is in good quantitative agreement with calculations based on the work of Tucker. It should make possible the construction of photon-noise-limited microwave heterodyne receivers.

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

“…The apparatus used for mixer measurements is the same as that described in previous publications 1 ' 4 . The helium bath temperature was generally 1.5K, although mixer efficiency varied only weakly with temperature for T<Tc/ 2 .…”

Superconductive devices for millimeter wave detection, mixing, and amplification

“…This effect does not appear to be troublesome in the quasiparticle mixers [37]. The noise in the Josephson mixer appears to be significantly larger than that in quasiparticle mixers.…”

“…The fit of the photon assisted tunneling theory to the mixer data just discussed has been examined in some detail to determine whether the predicted gain mechanism was in fact operative [37]. The input data for the model were a series of I-V curves like those in Fig.…”

Measurement of the noise contributions to SIS heterodyne receivers

“…This is important for predicting the mixer modifications necessary to further improve a mixer's performance. Without any knowledge of the absolute incident LO power level or coupling efficiency there is often a large range of embedding impedances which adequately fit the measured IV curve [12]. Knowing the coupling efficiency narrows the possible impedances to a small region of the Smith chart which can be compared with the intended design impedance.…”

“…The shape of the IV curve can be used to estimate the driving point impedance seen by the SIS junction [12], [13] and Tucker's theory can be used to calculate the mixer noise, T, , under the assumption that the embedding circuit is a lossless RF transformer from the signal input to the junction [14]. Our experience is that the driving point impedance is not usually determined accurately enough to yield a useful calculation of the RF coupling efficiency.…”