Superconducting submillimeter direct detector using high-frequency current noise

Boris S. Karasik, Bertrand Delaet, William R. McGrath +3 more

John D. Teufel, Minghao Shen, Luigi Frunzio +2 more

Seiichiro Ariyoshi, Hiroshi Matsuo, Chiko Otani +9 more

Hiroshi Matsuo, Sheng-Cai Shi, Takashi Noguchi +2 more

Development of two types of submillimeter-wave superconducting direct detectors are described. One is the SIS video detector and the other is the SIS photon detector. Using 500 GHz parallel connected twin junction device, video detector performance is eluted. High quantum efficiency in wide frequency range in submillimeter-wave and low noise performance is achieved. Noise equivalent power of 6 X 10-14 W/(root)Hz is measured at operating temperature of 1.5 K and bias voltage of 0.5 mV. Further improvements using distributed junction array is addressed. Large area niobium SIS junction (100 micrometer X 50 micrometer X 2) is used as a photon detection device and their thermal, electrical and optical performance is evaluated. Leakage current decrease more than three orders of magnitude at 0.5 K compared to that at 4.2 K. Noise of the device is limited by the shot noise.

Seiichiro Ariyoshi, Hiroshi Matsuo, Chiko Otani +4 more

We have developed submillimeter-wave direct detectors employing niobium-based superconducting tunnel junctions (STJs), with broadband spectral response, high sensitivity and imaging capability. Spectral response peaked at 650 GHz with a fractional bandwidth of 14 percent, which fits one of the important atmospheric windows for an astronomical project. We also confirmed the linearity of the detector response in the dynamic range greater than 10/sup 6/. The measured coupling efficiency was about 0.2, which was lower than the expected value of 0.5. The measured noise current of the detector was 10 fA//spl radic/Hz, which agreed with the shot noise from the residual leakage current of 100 pA at 0.3 K. Resultant noise equivalent power (NEP) is 1.6/spl times/10/sup -16/ W//spl radic/Hz, that is less than the background photon fluctuation limit for ground-based submillimeter-wave observations.

Semenov, A., Andreas Engel, Heinz‐Wilhelm Hübers +2 more

Advantage of superconducting photon detectors is a much lower noise in comparison to semiconductor counterparts. The purpose of the present work is to advance understanding of the physics of noises in a superconducting nanostructures. We have studied the rate and spectrum of dark counts of an 80-nm wide, 5-nm thick superconducting NbN meander-line and analyzed experimental data considering various noise mechanisms: quantum phase-slips, discrete thermodynamic fluctuations of the superconducting order parameter, and topological fluctuations in the two-dimensional vortex gas. The latter mechanism, i.e. Kosterlitz-Thouless phase transition, is the only one adequately describing the observed noise performance. Besides that, this approach provides clear explanation of the peculiarities of the resistive transition. The other two mechanisms would result in a much stronger current and temperature dependence of the dark count rate than the experiment shows. Basing on our understanding of the noise source, we propose a novel concept of a superconductor submillimeter direct detector. The detector operates in the superconducting state and utilizes current-dependent high-frequency electrical noise that changes under irradiation. The novel aspect is the use of the noise, which generally hampers the performance of conventional detectors, as the physical quantity that itself senses radiation. Predicted noise-equivalent power is 10_-13 W Hz_-1/2 at 4 K and should improve at lower temperatures.