Superconducting quantum detectors

Abstract:

Josephson-junction-based parametric amplifiers (JPAs) are key enabling technologies in superconducting quantum electronics, supporting applications ranging from dark-matter detection to quantum-computing readout. However, conventional JPAs are intrinsically narrowband, motivating the development of broadband architectures such as impedance-matched parametric amplifiers (IMPAs), which enhance bandwidth through the incorporation of auxiliary passive resonators.

In this work, we present the design and fabrication of a three-pole kinetic-inductance impedance-matched parametric amplifier (KIMPA) based on a niobium titanium nitride (NbTiN) nonlinear nanowire and implemented using an inverted microstrip architecture. The amplifier is synthesised using the multipole filter-design framework of Naaman and Aumentado and targets a 10% fractional bandwidth centred at 6 GHz with 20 dB gain. The device employs a multilayer architecture consisting of a 30 nm NbTiN wiring layer, a 150 nm amorphoussilicon dielectric layer, and a 200 nm niobium sky plane, enabling compact parallel-plate capacitors and improved fabrication robustness compared with conventional coplanar-waveguide implementations.

The design methodology is presented from the graph-based filter-synthesis model through circuit-level implementation and physical layout generation. Harmonic-balance simulations predict approximately 20 dB gain across a 6.0–6.4 GHz operating band, demonstrating the feasibility of broadband kinetic-inductance parametric amplification in an inverted microstrip platform. Fabricated devices have been completed and are currently being prepared for cryogenic characterisation.

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.