Superconducting quantum detectors

Abstract:

This paper describes a new Heterodyne Array Receiver Programme (HARP) and Auto-Correlation Spectral Imaging System (ACSIS) that have recently been installed and commissioned on the James Clerk Maxwell Telescope (JCMT). The 16-element focal-plane array receiver, operating in the submillimetre from 325 to 375 GHz, offers high (three-dimensional) mapping speeds, along with significant improvements over single-detector counterparts in calibration and image quality. Receiver temperatures are $\sim$120 K across the whole band and system temperatures of $\sim$300K are reached routinely under good weather conditions. The system includes a single-sideband filter so these are SSB figures. Used in conjunction with ACSIS, the system can produce large-scale maps rapidly, in one or more frequency settings, at high spatial and spectral resolution. Fully-sampled maps of size 1 square degree can be observed in under 1 hour. The scientific need for array receivers arises from the requirement for programmes to study samples of objects of statistically significant size, in large-scale unbiased surveys of galactic and extra-galactic regions. Along with morphological information, the new spectral imaging system can be used to study the physical and chemical properties of regions of interest. Its three-dimensional imaging capabilities are critical for research into turbulence and dynamics. In addition, HARP/ACSIS will provide highly complementary science programmes to wide-field continuum studies, and produce the essential preparatory work for submillimetre interferometers such as the SMA and ALMA.

Abstract:

The heating of SIS tunnel junctions by local oscillator (LO) power and bias voltage is well known and has been reported previously. In this paper, we present a novel method for recovering the heating parameters from the experimental pumped I-V curves of an SIS device at 700 GHz, together with the coupled LO power and the embedding impedance. Since this is obtained without assuming a particular power law between LO power and junction temperature, we will be able to find τeph, the electron-phonon interaction time of the superconducting material at various bath temperatures. We would deduce a power law that describes the dependence of the heat flow equation on temperature.

Abstract:

We present a new type of waveguide to microstrip transition designs for a 700 GHz SIS mixer. The transition comprised a unilateral finline taper and the RF power from the finline slot is coupled through coplanar waveguide to microstrip using two radial stubs. This transition is significantly easier to design and fabricate than the conventional antipodal finline taper since the fins do not overlap at any stage. A key feature of this design is that it can be deposited on Silicon-on-Insulator resulting in a finline mixer chip on approximately 15 µm silicon substrate. This allows the mixer chip to be held in the E-plane of the waveguide without a supporting groove in the waveguide wall, avoiding the excitation of higher order modes. The chip is simply supported by gold leads deposited on the substrate. It should be emphasized that the employment of such substrate will also decrease the loss and allow finline mixers design to be extended to the THz region.