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Quasiparticle heterodyne mixing in SIS tunnel junctions

P. L. Richards, T. M. Shen, R. Harris, Frances L. Lloyd

Published Oct 1, 1978• 1 citation
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Abstract

The rapid onset of quasiparticle tunneling current in superconductor-insulator-superconductor (Josephson) junctions at voltages above 2 delta/e is being used for millimeter wave heterodyne mixing. Junctions with 2 micron diameter and RN = 50 ohms have little capacitive shunting at the signal frequency of 36 GHz. Because there is no series resistance, residual capacitance can be tuned out. Single sideband conversion efficiencies of 0.18 and mixer noise temperatures as low as TM approximately 14K have been observed. Both results agree with shot noise limited mixer theory. Photon assisted tunneling effects are seen which indicate the approach to photon noise limited operation. (Author)

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The rapid onset of quasiparticle tunneling current in superconductor-insulator-superconductor (Josephson) junctions at voltages above 2 delta/e is being used for millimeter wave heterodyne mixing. Junctions with 2 micron diameter and RN = 50 ohms have little capacitive shunting at the signal frequency of 36 GHz. Because there is no series resistance, residual capacitance can be tuned out. Single sideband conversion efficiencies of 0.18 and mixer noise temperatures as low as TM approximately 14K have been observed. Both results agree with shot noise limited mixer theory. Photon assisted tunneling effects are seen which indicate the approach to photon noise limited operation. (Author)
The rapid onset of quasiparitcle tunneling current in superconductor-insulator-superconductor (Josephson) junctions at voltages above 2Δ/e is being used for millimeter-wave heterodyne mixing. Junctions with a 2-μm diameter and RN=50 Ω have little capacitive shunting at the signal frequency of 36 GHz. Because there is no series resistance, residual capacitance can be tuned out. Double sideband conversion efficiencies of 0.32 and mixer noise temperatures as low as TM⩽7 K=4hν/k have been observed. The results are compared with shot-noise-limited mixer theory. Photon-assisted tunneling effects are seen which indicate the approach to photon-noise-limited operation.
A computer simulation is constructed to describe the performance of superconductor-insulator-superconductor (SIS) quasiparticle heterodyne receivers in terms of photon-assisted tunneling theory. The results predict that conversion efficiencies greater than unity can be realized at millimeter wave frequencies, with noise temperatures approaching the fundamental quantum limit. The nonlinearity responsible for the mixing is the extremely rapid onset of quasiparticle tunneling current in SIS junctions near the full gap voltage 2Δ/e, and is independent of the Josephson pair currents. Substantial gain is expected under a variety of conditions and for a wide range of source and load impedances.
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.
Single particle (quasiparticle) tunneling through an insulating barrier between two superconductors or between a superconductor and a normal conductor is being used to make very low noise detectors and mixers for millimeter wavelengths. The nonlinearity of the I-V curve obtained from tunneling between two superconductors can be so strong that classical theory breaks down and photon assisted tunneling theory must be used to understand device performance. Quantum theory predicts that a quasiparticle tunnel junction can be operated as a microwave photon detector with quantum efficiency close to unity or as a heterodyne mixer with conversion gain and with mixer noise temperature comparable with the quantum noise limit T sub M = h omega/k. Both of these predictions have been experimentally realized at 36GHz using superconductor-insulator-superconductor junctions. It appears probable that these quasiparticle detectors and mixers will supercede the corresponding Josephson effect devices at millimeter wavelengths. (Author)
Single-particle (quasi-particle) tunneling through an insulating barrier between two superconductors or between a superconductor and a normal conductor is being used to make very-low-noise detectors and mixers for millimeter wavelengths. The nonlinearity of theI-Vcurve obtained from tunneling between two superconductors can be so strong that classical theory breaks down and photon-assisted tunneling theory must be used to understand device performance. Quantum theory predicts that a quasi-particle tunnel junction can be operated as a microwave photon detector with quantum efficiency close to unity or as a heterodyne mixer with conversion gain and with mixer noise temperature comparable with the quantum noise limitT_{M} =\bar{h}\omega/k. Both of these predictions have been experimentally realized at 36 GHz using superconductor-insulator-superconductor (SIS) junctions. It appears probable that these quasi-particle detectors and mixers will supercede the corresponding Josephson-effect devices at millimeter wavelengths.
We report operation of superconductor-insulator-superconductor quasiparticle tunnel junctions as mixers and detectors at millimeter wavelengths. The voltage scale of the nonlinearity in the I-V curve of such junctions can be small enough that classical device theory breaks down. Calculations based on photon assisted tunneling theory are then necessary to understand the observed performance. The performance predicted in this novel regime is sufficiently good that practical applications appear very promising. The best mixer result observed at 36 GHz is a double side-band mixer noise temperature Tm≤ 7 K which is about 4 times the photon noise limited value of hv/k. When operated as a direct detector, a current responsivity of 3,500 A/W was observed. This is half the quantum limited value e/hv, which corresponds to one tunneling electron for each incident microwave photon. The best observed NEP was 3 × 10-16W√Hz.