Superconducting quantum detectors

Abstract:

We report the design of a compact dual-polarization on-chip superconductor–insulator–superconductor receiver for array applications. The planar-circuit receiver chip is comprised of the entire radio frequency (RF) signal processing chain with three main circuit components alongside some auxiliary circuits: (1) a polarization splitting 4-probe orthomode transducer (OMT) that couples the RF and local oscillator signal from free space to the chip via a drilled feedhorn; (2) two hybrids that recombine the power of each polarization from the two sets of orthogonal OMT probes; and (3) twin-junction Nb/AlOx/Nb mixers that downconvert the recombined signals to the intermediate frequency. We ensure that the four side walls of each pixel are free from obscuration, using only the top and bottom of the pixel for various connections. Consequently, the design is extendable to a large format array. In this paper, we present the detailed design of the on-chip receiver, including extensive heterodyne simulations and its potential extension into a large format array.

Abstract:

We present the design of a superconductor-insulatorsuperconductor (SIS) mixer fed with a 2-probe antenna mounted in a circular waveguide, hence avoiding the need for a rectangular waveguide that is often difficult to machine at high millimetre and sub-millimetre frequencies. The mixer is designed to operate from 275–375 GHz, covering a similar frequency range to the HARP-B receiver of the James Clerk Maxwell Telescope. Each antenna probe is connected to a separate but identical mixer circuit comprising three SIS junctions connected in series to reduce the parasitic capacitance, and the relevant tuning circuits and RF chokes. The down-converted IF power at the output of each mixer branch is expected to be combined using either a microwave Wilkinson power combiner or a 180◦ hybrid, to recover the full signal strength. In this paper, we present in the detail the electromagnetic simulations of each RF component making up the mixer chip, as well as the performance of the entire 2-probe mixer including the RF and IF performance predicted using SuperMix, a software package developed based on Tucker’s theory of quantum mixing. Finally, we show how such circular waveguide SIS mixers can be easily populated onto a simple split-block to form a 16-pixel array.