Dr Nikita Klimovich

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.

Abstract:

Traveling wave parametric amplifiers (TWPAs) offer the most promising solution for high gain, broadband, and quantum noise limited amplification at microwave frequencies. Experimental realization of TWPAs has proved challenging with often major discrepancies between the theoretically predicted and the measured gain performance of the devices. Here, we extend the conventional modeling techniques to account for spatial variation in the surface impedance of the thin film and the parametric sum-frequency conversions effect, which subsequently results in accurate reproduction of experimental device behavior. We further show that such an analysis may be critical to ensure fabricated TWPAs can operate as designed.

Abstract:

It is expected that the operation of microwave Kinetic Inductance Travelling Wave Parametric Amplifiers (KITWPAs) can be extended to the millimetre (mm) and the sub-mm wavelength range as long as the frequency is below the gap frequency of the superconducting film. This paper presents possible mm-wave designs for KITWPAs based on microstrip transmission lines. Our device is designed based on the BCS (Bardeen-Cooper-Schrieffer) model which successfully reproduces the measured transmission profile, gain, bandwidth, and nonlinear response of a fabricated KITWPA operating in the Ka-band, and includes the millimetre-wave dielectric loss determined by fitting the quality factor of a Wband microstrip resonator. We suggest a layout for a KITWPA operating near 220 GHz that can be fabricated using the same superconducting properties as the Ka-band device and can be coupled to a waveguide system. We conclude the paper by extending the 220 GHz design to higher frequency regimes approaching 1 THz.

Abstract:

Travelling wave parametric amplifiers (TWPAs) made from highly nonlinear reactive superconducting thin films have been demonstrated to be a potentially viable quantum-noiselimited amplifier technology for various fundamental physics platforms, including microwave/millimetre (mm)/sub-mm astronomy, dark matter search experiments, absolute neutrino mass determinations, and qubit readout platforms. To date, only a limited number of successful kinetic inductance (KI-)TWPA devices have been reported, with the majority of them fabricated from niobium titanium nitride (NbTiN) thin films; although in principle, any highly nonlinear low loss superconducting film can be used to construct a KITWPA. In this proceeding, we explore the suitability of using a different type of superconducting film, titanium nitride (TiN) for such application. We report on the detailed analysis of the nonlinear behaviour of TiN films to ascertain the film’s suitability for application as KITWPA. We experimentally characterised TiN transmission lines at cryogenic temperatures to compare the results predicted with electromagnetic simulations. This characterisation and analysis allows us to understand the fundamental physics governing the behaviour of the TiN films, their merits and limitations, and whether they are well suited for applications as KITWPAs.

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.