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NASA STI/Recon Technical Report N

SIS Quasiparticle Junctions As Microwave Photon Detectors

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

Published Oct 1, 1979• 3 citations
OpenAlex

Abstract

The strong nonlinearity of the quasiparticle tunneling current in superconductor-insulator-superconductor junctions near the full gap voltage 2 Delta/e can be used for direct detection of microwave signals. Measurements at 36 GHz yielded a current responsivity of 3,5000 A/W, which is within a factor of 2 of the quantum limited value e/h-bar omega. The measured NEP of 2.6 + or - 0.8 x 10 to the -16th power W/sq-rt. Hz is the lowest value reported to date and can probably be improved significantly. The experimental results are compared with both the standard classical analysis and photon assisted tunneling theory. (Author)

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Applied Physics Letters•Mar 1, 1979•164 citations
The strong nonlinearity of the quasiparticle tunneling current in superconductor-insulator-superconductor junctions near the full gap voltage 2 Delta/e can be used for direct detection of microwave signals. Measurements at 36 GHz yielded a current responsivity of 3,5000 A/W, which is within a factor of 2 of the quantum limited value e/h-bar omega. The measured NEP of 2.6 + or - 0.8 x 10 to the -16th power W/sq-rt. Hz is the lowest value reported to date and can probably be improved significantly. The experimental results are compared with both the standard classical analysis and photon assisted tunneling theory. (Author)
The strong nonlinearity of the quasiparticle tunneling current in superconductor-insulator-superconductor junctions near the full-gap voltage 2Δ/e can be used for direct detection of microwave signals. Measurements at 36 GHz yielded a current responsivity of 3500 A/W, which is within a factor of 2 of the quantum-limited value e/∇ω. The measured NEP of 2.6±0.8×10−16 W/,Hz1/2 is the lowest value reported to date and can probably be improved significantly. The experimental results are compared with both the standard classical analysis and photon-assisted tunneling theory.
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.
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.
Quasiparticle mixers have shown strong quantum effects, conversion gain, and noise levels approaching the quantum limit, but only in tunnel junctions with very low sub-gap "leakage" conductance. It has been suggested that SIS' tunnel junctions, made from two different conductors with unequal gaps, will function as high gain mixers since the dynamic conductance below the gap is negative. We report results of the first SIS' mixing and direct detection experiments. At 36 GHz, a conversion efficiency of -4 dB with a noise temperature of 33 K (SSB) has been obtained. A novel gain mechanism for SIS' direct detectors is predicted. A direct detector responsivity of 250 A/W was measured. We compare our results to quantum theory models. In addition, we demonstrate quasiparticle harmonic mixing of a 36 GHz signal with an 18 GHz local oscillator in tin SIS junctions. Harmonic mixers can have important advantages at high microwave frequencies where insufficient local oscillator power is available.
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.