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:

Microwave superconducting Josephson Travelling Wave Parametric Amplifiers (JTWPAs) exploit the non-linear inductance of a long superconducting metamaterial line formed by thousands of Josephson junctions to achieve broadband parametric gain with quantum limited added noise. Nevertheless, pin-holes in the dielectric (spacer) layer required for fabricating these superconducting transmission lines (STLs) represent a challenge for JTWPAs fabrication. In this paper, we explore two pin-holes mitigation techniques, which shown promising results with DC characterisation of a suite of test structures at cryogenic temperatures. When implemented for actual JTWPA designs with much longer length, they have shown to improve the fabrication yield albeit some pin-holes still seems to exist over the large wafer area. This indicates that further mitigation effort is required to completely eradicate the pin-holes issue for applications requiring large area of dielectric layer such as microwave JTWPAs.

Abstract:

We present a planar Yagi antenna that has an end-fire beam characteristic and broad operational bandwidth. Two dipoles with different lengths are cascaded together to broaden the bandwidth. Printed directors and truncated ground plane are employed to achieve high front-to-back gain ratio. The double-dipole antenna is fed directly with a microstrip, and hence is readily adaptable to most of the millimetre and sub-millimetre detector circuits. In this paper, we present the antenna design in the context of designing a 1.05 THz Superconductor-Insulator-Superconductor (SIS) mixer that is suitable for Atacama Large Millimetre/Sub-millimetre Array (ALMA) Band 11 receiver. Detailed analysis of the antenna design is discussed, and simulated far field beam patterns and bandwidth performance is presented.

Abstract:

Travelling wave parametric amplifiers (TWPAs) made from highly nonlinear reactive superconducting thin films have been demonstrated to be a viable technology for various quantum applications, including fundamental physics experiments such as astronomy and axion dark matter searches, as well as commercial applications like quantum computational and communication systems. In this paper, we present the design of a kinetic inductance TWPA comprising a patterned titanium nitride film that can operate at 0.3 K to demonstrate the feasibility of operation closer to 1 K temperature, paving the way to achieve even higher bath temperature operation. We discuss in detail the design of our TWPA, along with the predicted gain-bandwidth product and other characteristics. We perform the preliminary experimental investigation of the thin film properties and compare that with the simulated results. We found that there are several discrepancies between the measured and the predicted behaviour of the thin film. We attribute these differences to the fact that the fabricated thin film has a different gap voltage, resistivity and thickness to what we expected. With a new set of estimated parameters, we successfully reproduce the measured transmission profile. We further show that by utilising bridges to ensure equipotential grounds for the CPW lines, we managed to reduce the rippling effect and achieve higher gain with broader bandwidth. We expect that our TWPA can achieve higher than 20 dB gain from approximately 0–8 GHz.