Superconducting quantum detectors

Abstract:

In this paper, we present our latest works on developing the various generic technologies to find the innovative solutions for constructing a heterodyne focal plane array, based on the Superconductor-Insulator-Superconductor (SIS) mixer technology. This includes the use of the planar superconducting circuit technology to replace the commonly used bulky waveguides or optical components, therefore simplifying the radio frequency (RF) operation and minimising the size of the array. We will describe the design of a novel easy-to-machine feed horn technology which enables deployment of large arrays with minimal cost. This technology has been demonstrated successfully and has since been deployed in various existing and up-coming telescopes. We then demonstrate these capabilities by presenting the design and built of a small pixel-count array near 220 GHz range, combining both the E- and H-polarisation chains within a single mixer block. Finally, we briefly describe our recent works on the superconducting parametric amplifier technology that could potentially replace the conventional semiconductor amplifiers that are power hungry and dissipate large amount of heat, which render the construction of large arrays difficult.

Abstract:

Travelling Wave Parametric Amplifiers (TWPAs) can potentially achieve quantum limited noise over a broad bandwidth in the microwave regime, with potential applications in the readout of millimetre (mm) and sub-millimetre (sub-mm) receivers to further improve the system sensitivity, among many other applications. TWPAs using embedded Josephson junctions (J-TWPA) have proven to exhibit noise performance approaching the quantum limit, however its compression point (P–1dB ~ –100 dBm) is too low for reading out mm and sub-mm astronomical receivers. Therefore, we explored the design of higher dynamic range JTWPAs to match the power requirements, and to optimise the performances of the JTWPA for this specific application. Our aim is to adapt the well-established Nb-AlOx-Nb tri-layer fabrication technique used routinely for developing high-quality Superconductor-Insulator-Superconductor (SIS) tunnel junctions to fabricate our JTWPA. Therefore, we present in this paper our investigation of the feasibility of such technique in fabricating large number of lower critical current density junctions embedded in a coplanar waveguide (CPW). The preliminary results on a 500-junctions device are in line with the expected behaviour, showing a measured gain consistent with theoretical calculations which demonstrates the potential use of the tri-layer tunnel junction technology for the fabrication of JTWPAs.

Abstract:

Travelling wave parametric amplifiers (TWPAs) made from highly nonlinear reactive superconducting thin films have been demonstrated to be a potentially viable quantum-noiselimited amplifier technology for various fundamental physics platforms, including microwave/millimetre (mm)/sub-mm astronomy, dark matter search experiments, absolute neutrino mass determinations, and qubit readout platforms. To date, only a limited number of successful kinetic inductance (KI-)TWPA devices have been reported, with the majority of them fabricated from niobium titanium nitride (NbTiN) thin films; although in principle, any highly nonlinear low loss superconducting film can be used to construct a KITWPA. In this proceeding, we explore the suitability of using a different type of superconducting film, titanium nitride (TiN) for such application. We report on the detailed analysis of the nonlinear behaviour of TiN films to ascertain the film’s suitability for application as KITWPA. We experimentally characterised TiN transmission lines at cryogenic temperatures to compare the results predicted with electromagnetic simulations. This characterisation and analysis allows us to understand the fundamental physics governing the behaviour of the TiN films, their merits and limitations, and whether they are well suited for applications as KITWPAs.