Dr. Boon Kok Tan

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:

Superconducting travelling wave parametric amplifiers (TWPAs) exhibit great promise across various applications, owing to their broadband nature, quantum-limited noise performance, and high-gain operation. Whilst their construction is relatively simple, particularly for thin-film-based TWPAs, challenges such as the requirement for an extremely long transmission line, current fabrication limitations, and their sensitivity to fabrication tolerances, mean that their optimal operating conditions often differ from those anticipated during the design stage. As a result, manual fine-tuning of numerous operational parameters becomes necessary to recover optimal performance; a process that is both labour-intensive and time-consuming. This paper introduces an automated methodology designed to significantly accelerate the characterisation of a TWPA by several orders of magnitude without requiring human intervention. Additionally, we have developed metrics to condense the multitude of measured frequency responses of the TWPA, obtained in data cube form, into an easily-understandable format for further scientific interpretation. To demonstrate the efficacy and speed of our methodology, we utilise an existing NbTiN (niobium titanium nitride) TWPA as an example. This showcases the capability of our approach to unveil both broad- and fine-scale behaviours of the device, highlighting the importance of an automated experimental setup for the in-depth investigation of TWPAs for future developments.

Abstract:

The well-established technology of the superconducting quantum parametric amplifier (SPA) can be reconfigured to perform functions beyond amplification, such as frequency multiplication, by utilising the low-noise, low-loss superconducting nonlinear transmission line. This versatile technology holds potential for various applications, including ‘pumping’ a millimetre (mm) or sub-mm wave heterodyne mixer or driving a high-frequency SPA. Its significance lies in the ability to incorporate a high-purity signal source into the cryogenic stage alongside the primary detector, thereby eliminating noise associated with room temperature sources. Additionally, there is potential for on-chip integration with the detector circuit, leading to a more compact architecture.
This manuscript details the design of a travelling-wave parametric multiplier (TWPaM) that exploits the nonlinear wave-mixing mechanism to enhance the third harmonic growth from a strong pump tone injected into the travelling wave parametric amplifier (TWPA)-like device. While this functionality has been demonstrated previously, it exhibited narrowband performance. In this manuscript, we present our approach to designing a dispersion engineering scheme that enables the generation of broadband tunable tripler tones with high conversion efficiency. We showcase our design methodology using a niobium titanium nitride (NbTiN) high-gap thin-film transmission line as an example. Our presentation includes the theoretical model governing the physics of higher harmonics generation, emphasising phase-matching conditions that allow for broadband operation while suppressing unwanted modes. Although the ultimate aim is to develop a mm/sub-mm TWPaM, we aim to demonstrate the feasibility of their operation with a scaled microwave design in this manuscript. We will show that we can theoretically achieve close to 35% conversion efficiency across approximately 60% operational bandwidth.