Superconducting quantum detectors

Abstract:

A new 1x4 focal plane array centered around 230 GHz is presented in this paper. The size of the array was limited to 4 pixels due to the space available in the test cryostat; however, we can expand the design in the future. On the front of the array block there are 4 waveguides flanges for the RF feed horns, while the local-oscillator signal enters through a separate waveguide on the side. The local-oscillator power is multiplexed using cascaded E-plane power dividers and then combined with the RF signals using directional couplers. Preliminary tests of the array block have now been completed. They show reasonable local-oscillator distribution and excellent RF signal isolation. Future work will involve testing the noise properties of the array block and improving the local-oscillator distribution.

Abstract:

We present a new software package for simulating the performance of Superconductor / Insulator / Superconductor (SIS) mixers. The package is called QMix (“Quasiparticle Mixing”) and it uses multi-tone spectral domain analysis (MTSDA) to calculate the quasiparticle tunneling current through the SIS junction. This technique is very powerful and it allows QMix to simulate multiple strong tones and multiple higher-order harmonics. We have compared this software to the experimental data from a 230 GHz SIS mixer, both to validate the software and to explore the measured results. Overall, we found very good agreement, demonstrating that QMix can accurately simulate the performance of SIS mixers. We believe that QMix will be a useful tool for analyzing experimental data, designing new SIS mixers, and simulating new applications for SIS junctions, such as frequency multiplication.

Abstract:

In this paper, we present preliminary measured performance of an SIS mixer employing a Nb/AIN/NbN tunnel junction in the frequency range of 780–950 GHz range. The mixer design is an upgrade of the Carbon Heterodyne Array of the Max-Planck-Institute Plus (CHAMP+) mixer, coupled with an easy to fabricate smooth-walled horn. The noise temperature of the mixer is measured using the standard Y-factor method, but all the RF optics is enclosed in the cryostat. We use a rotating mirror in the cryostat to switch between a room temperature load and a 4 K blackbody load. With this method, we have measured a noise temperature of 330 K around 850 GHz, corrected for a mismatch between a reduced height rectangular waveguide at the input of the mixer block and a full height waveguide at the output of the horn. To remove this mismatch we now plan to redesign a new mixer chip with a full-height waveguide backpiece. The expected performance of the new mixer chip is also reported.