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Journal of Applied Physics

Sensitivity of Josephson junctions in video detection of microwave and millimeter-wave radiation

Hiroshi Ohta

Published Dec 1, 1972• 12 citations
Publisher

Abstract

The responsivity and the noise equivalent power (NEP) of Josephson junctions in video detection of microwave and millimeter-wave radiation have been calculated. The sensitivity to radiation is assumed to be limited by the rounding of the voltage-current curve due to thermal noise of both the source resistance and the junction resistance. The calculated NEP is at least several tens of times better than any experimentally established.

DOI
10.1063/1.1661090

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Proceedings of the IEEE•Jan 1, 1973•18 citations
The responsivity and the noise equivalent power (NEP) of Josephson junctions in video detection of microwave and millimeter-wave radiation have been calculated. The sensitivity to radiation is assumed to be limited by the rounding of the voltage-current curve due to thermal noise of both the source resistance and the junction resistance. The calculated NEP is at least several tens of times better than any experimentally established.
Résumé. 2014 On calcule la température de bruit et la température minimum détectable d’une jonction Josephson soumise à un rayonnement millimétrique en utilisant l’équation de Fokker-Planck. La température de bruit obtenue peut être très voisine de la température ambiante. Un récepteur pour radiotélescope à très large bande utilisant une jonction Josephson peut avoir une température minimum détectable inférieure à celle d’un maser à ondes progressives. Abstract. 2014 The noise temperature and the minimum detectable temperature of a Josephson junction in video detection of microwave and millimeter-wave radiation has been calculated. We use the well-known method based on a Fokker-Planck equation. The noise temperature can be very close to ambient temperature. Because its predetection bandwidth is very wide, a Josephson-effect radio telescope receiver can have a minimum detectable temperature better than that of a traveling-wave maser. REVUE DE PHYSIQUE APPLIQUÉE TOME 9, JANVIER 1974, PAGE We apply monochromatic radiation to a Josephson junction to determine the frequency dependence of the response. We use a phenomenological model for a Josephson junction, with signal radiation and current noise, described by the equations: These are standard symbols and are given in reference [1]. R is the parallel combination of the junction resistance and the source resistance. The noise current has a white spectum A very important assumption is that the capacitance is small We treat the radiation as a perturbation. The solu-tion of the unperturbed equation without radiation or noise is the voltage-current curve
Millimeter-wave detection was investigated using a step-edge microbridge Josephson junction fabricated by a YBaCuO thin film for both the video detection and harmonic mixing detection. Current–voltage (I–V) characteristics, which could be described by the resistively shunted junction (RSJ) model, were obtained up to 70 K with the IcR product of 150 μV at 70 K. The responsivity and noise equivalent input power were calculated as 2400 W/V and 4.4×10−14 W/√Hz, respectively, in the video detection assuming the RSJ model approximation. Clear dependence of the intermediate frequency output on the applied dc bias voltage was observed in the harmonic mixing detection with the harmonic numbers of 5–16, reflecting the change of dynamic resistance at the constant voltage steps induced by the local oscillation signal on the I–V curve. A minimum detection power of −59.4 dB m and a conversion efficiency (η) of −49.6 dB were obtained for the harmonic number (N) of 5 at 60 K. The relationship between the η and N was expressed as η∝N−2.2.
Current-biased Josephson junctions can act as detectors of electromagnetic radiation. At optimal conditions, their sensitivity is limited by fluctuations causing stochastic switching from the superconducting to the resistive state. This work provides a quantitative description of a stochastic switching current detector, based on an underdamped Josephson junction. It is shown that activation of a Josephson plasma resonance can greatly enhance the detector responsivity in proportion to the quality factor of the junction. The ways of tuning the detector for achieving optimal operation are discussed. For realistic parameters of Nb / Al O x / Nb tunnel junctions, the sensitivity and noise-equivalent power (NEP) can reach values of S ≃ 5 × 10 12 (V/W) and NEP ≃ 2 × 10 − 23 ( WHz − 1 / 2 ), respectively. These outstanding characteristics facilitate both bolometric and single-photon detection in microwave and terahertz ranges. Published by the American Physical Society 2024
Detection mechanisms in Josephson junctions with energies Ej comparable to thermal energies kT have been studied. The responses ΔV of YBa2Cu3O7−x bicrystal junctions to monochromatic radiation with frequencies f ranging from 94 GHz to 3.1 THz can be described in terms of classical rectification on a static nonlinear V–I curve at low frequencies and frequency modulation of the ac Josephson current at high frequencies, with an interplay between these mechanisms at intermediate frequencies. An electrical noise-equivalent power of (9 ± 3) × 10−15 W/Hz1/2, a responsivity of (3.4 ± 0.5) × 105 V/W, and a dynamic power range of 5 × 104 have been demonstrated for the square-law classical detection of 94 GHz radiation with the junctions at 50 K. The effect of background radiation on the V–I curves of YBa2Cu3O7−x bicrystal junctions was found to have an optical noise-equivalent temperature of ≤30 mK/Hz1/2. The main contribution to the effect comes from the interplay between the classical and Josephson detection mechanisms. The spectral and power dependencies of the responses ΔV of Josephson junctions have been numerically simulated within the resistively shunted junction model at various values of kT/Ej, and the results are in acceptable agreement with the experimental data.
A millimeter and submillimeter microwave source is described in which a point-contact Josephson junction is used as both the emitter and as a homodyne detector of the microwave radiation. The microwave radiation is conveyed from the Josephson junction to the room-temperature environment outside the Dewar of liquid helium by an oversize waveguide. A room-temperature Fabry-Perot resonator refocuses the radiation on the oversize waveguide which returns the radiation to the emitting junction which also serves as a coherent detector with sensitivity 10-15W/√Hz. The detector is sufficiently sensitive that the emitted power of 10-12W can be detected with high signal-to-noise ratio. Power required by the junction is of the order 10-6W from the bias supply. For the experiments reported, the wavelength of the emission could be varied over discrete wavelengths between 1.1 and 2.6 mm by varying the voltage bias across the junction. These wavelengths corresponded to the resonant frequencies of a cavity tightly coupled to the Josephson junction, and the frequencies can be changed by modifying the geometry of the cavity.