Superconducting quantum detectors

Abstract:

Kinetic inductance travelling-wave parametric amplifiers (KITWPAs) have emerged as promising quantum-limited amplifiers for large-format detector arrays and quantum sensing applications. Extending this technology to millimetre-wave frequencies could enable ultra-low-noise pre-amplification for astronomical heterodyne receivers, potentially improving receiver sensitivity and mapping speed. In this work, we present the preliminary design of a W-band three-wave mixing (3WM) KITWPA based on a high-kinetic-inductance niobium-titaniumnitride (NbTiN) inverted microstrip transmission line.

The proposed architecture incorporates waveguide-coupled radial-probe transitions and a DC-bias network adapted from established superconducting mixer technologies to enable 3WM operation at millimetre-wave frequencies. Electromagnetic simulations are combined with coupled-mode analysis to evaluate the amplifier performance. Simulations predict an intrinsic gain exceeding 20 dB over a broad frequency range from 30 to 110 GHz. When integrated within a WR-10 waveguide environment, the effective operating bandwidth is predicted to extend from 75 to 110 GHz with more than 15 dB gain. The proposed design demonstrates the feasibility of implementing DC-biased 3WM KITWPAs in the W-band and represents a potential route towards low-noise pre-amplifiers for future mm-wave and submm-wave heterodyne receiver systems.

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 the design and performance analysis of waveguide-based superconductor–insulator–superconductor (SIS) mixers employing niobium titanium nitride (NbTiN) transmission lines and tunnel junctions comprising niobium/aluminium oxide (Nb/AlO_x/Nb) or niobium/aluminium nitride (Nb/AlN/Nb) topologies. These superconducting quantum devices are developed to enable wideband heterodyne operation for next-generation far-infrared (FIR) space missions in the sub-terahertz regime. The mixer circuits are optimised for simultaneous broadband radio-frequency (RF) and intermediate-frequency (IF) operation using microstrip architectures that incorporate end-stub, end-loaded, and twin-junction tuning networks. Threedimensional electromagnetic simulations, combined with quantum-mixing analyses, predict receiver noise temperatures approaching four times the quantum limit across 0.50–0.79 THz for the AlO_x-based design. The AlN-based variant further extends the RF coverage to 0.39–0.82 THz, satisfying the requirements of several proposed space missions while overlapping the Atacama Large Millimetre/sub-millimetre Array (ALMA) Bands 8 and extended Band 9. These simulated results demonstrate that NbTiN-based microstrip SIS mixers have the potential to deliver high sensitivity and wide instantaneous bandwidth at sub-terahertz frequencies, establishing them as strong candidates for next-generation space-borne and ground-based FIR observatories.