Superconducting quantum detectors

Abstract:

<jats:title>Abstract</jats:title> <jats:p>The Atacama Large Millimetre/Sub-millimetre Array (ALMA) wideband sensitivity upgrade (WSU) project marks the next milestone in the development of millimetre (mm) and sub-mm astronomy. In this paper, we present the design, optimisation, and performance analysis of the ALMA Band-9 superconductor-insulator-superconductor (SIS) mixer for applications in the upcoming WSU programme, and other high-frequency astronomical observations. The mixers feature a niobium radial-rectangular probe antenna integrated with a silicon-on-insulator (SOI) substrate, which ensures minimal RF power leakage and optimised power coupling. We base our mixer design on conventional aluminium oxide (AlO<jats:sub> <jats:italic>x</jats:italic> </jats:sub>) tunnel junction technology, with a critical current density of about 10 kA cm<jats:sup>−2</jats:sup>. We explore the impact of different junction sizes on the radio frequency (RF) and intermediate frequency (IF) bandwidths. We demonstrate that the new mixer design is capable of meeting the more stringent sensitivity-bandwidth requirements of the ALMA-WSU programme over the original Band-9 frequency range (602–720 GHz), as the IF bandwidth performance reaches up to 20 GHz. The IF bandwidth improvement is approximately double that of the current existing ALMA Band-9 mixers. These results suggest that our mixer designs provide a promising solution for future ALMA upgrades and other high-frequency applications requiring broad RF and IF bandwidth.</jats:p>

Abstract:

Superconducting travelling-wave parametric amplifiers (TWPAs) play a vital role in a range of high-sensitivity applications. These devices can be realised using various superconducting materials, such as high kinetic inductance films or low-loss transmission lines embedded with discrete nonlinear elements like Josephson junctions (JJs) or superconducting quantum interference devices (SQUIDs), and can operate across different wave-mixing regimes. However, a unifying framework for quick assessment and thus efficiently evaluating the performance of these diverse TWPA architectures, particularly during the design phase, remains lacking. Most existing models are derived from first principles for specific TWPA designs and lack general applicability. While certain simulation program with integrated circuit emphasis (SPICE) tools can more accurately emulate TWPA behaviour post-design, they are typically computationally intensive, time-consuming, and offer limited physical insight; especially regarding key performance-determining factors such as phase matching. This, in turn, impedes the rapid identification of optimal TWPA configurations. In this work, we extend a previously introduced framework for kinetic-inductance (KI-) TWPAs and demonstrate its applicability to a broader class of χ(3)-type TWPA configurations, including bare JJ (JTWPA) and symmetric SQUID-based TWPAs, operating in all wave-mixing modes. This approach facilitates rapid design-space exploration prior to detailed optimisation using SPICE-based simulations. Our method accommodates a wide range of unit cell topologies and meta-material parameters without requiring ground-up derivations from first principles. We validate the framework by comparing it against representative models from the literature, including JJ-, KI-, and DC SQUID-based TWPA designs, and show that it reliably captures the first-order behaviour of their gain–bandwidth characteristics.

Abstract:

The Heterdyne Spectrometer Instrument (HSI) is one of two instruments on the Far-IR Spectroscopy Space Telescope (FIRSST) proposal to NASA. It would be the first heterodyne array receiver in space and has 3 frequency bands, each containing two 5-pixel arrays, one per polarizations. HSI uses high TRL (>6) components and is an innovative, but low-risk instrument.