Superconducting quantum detectors

Abstract:

Superconducting detectors are set to become the principal method by which wide-field mapping and deep point-source searches are carried out throughout the whole of the submillimetre-wave frequency range. In the paper, we outline the operation of the basic detector types, and assess the future of superconducting detector technology. We place particular emphasis on distinguishing between single-mode, few-mode, and multi-mode designs, and we explain how similar the superconducting bolometer and mixer technologies have become. We outline the considerable advances that are taking place in the area of superconducting detector technology.

Abstract:

In this paper, we describe the design and operation of a 350-GHz flnline superconductor-insulator-4superconductor mixer. The mixer is fed by a horn-reflector antenna, and the superconducting circuit is fabricated using planar-circuit technology and fully integrated tuning. An important feature of the mixer is that it employs an antipodal flnline section, deposited on one side of a quartz substrate, which transforms the high impedance of the waveguide (300 fi) to the low impedance of the microstrip (-420 II). The Nb/Al-oxide/Nb tunnel junction is fabricated at the same time as the flnline circuit. In this paper, we describe the design procedure in some detail. We pay particular attention to the synthesis of the flnline taper and the electromagnetic design of the horn-reflector antenna. We have tested a flnline mixer over the frequency range of 330-370 GHz and measured a receiver noise temperature of 90 K, which remained unchanged over the whole frequency range. Our investigation has demonstrated that it is possible to make superconducting flnline mixers for frequencies as high as 350 GHz. © 2000 IEEE.

Abstract:

We present a new method to determine the contribution of the IF-amplifier chain to the overall noise performance of an SIS-based receiver. Using simulated I-V and IF power characteristics, we show that the standard method used to date to evaluate the IF noise can underestimate the contribution because of non-negligible curvature in the post-gap SIS I-V characteristic. We demonstrate that the new method is not susceptible to the post-gap curvature, and discuss its benefits and limitations to the accurate and precise evaluation of IF noise contributions.

Abstract:

Astronomical interest in millimetre and submillimetre wavelengths (f = 300 GHz to 1 THz) has fuelled the development of low noise high sensitivity detectors for these wavelengths. HARP (Heterodyne Array Receiver Project) will be a 16 element focal plane imaging array of heterodyne detectors for the 850 micron (325 - 375 GHz) band. Each element will consist of a mixer employing an SIS (superconductor - insulator - superconductor) tunnel junction as the non linear device. When attached to the James Clerk Maxwell Telescope in Hawaii the array will offer greatly improved mapping speeds of extended objects complementing existing bolometer detectors and planned millimetre wave aperture synthesis telescopes. This presentation will examine aspects of the SIS device physics, quasi-optics, and electromagnetic design for the HARP imaging array. Original results from computer modelling and experiments on a prototype mixer will be presented.