Broadband tuneable travelling wave parametric multiplier based on high-gap superconducting thin film

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.