Quantum-Limited Amplifiers for Detector Arrays on NASA's Inflation Probe

During the fellowship period, I worked on the development of the Traveling-wave Kinetic Inductance Parametric (TKIP) Amplifier. This superconducting amplifier, operating at GHz frequencies, can, in theory, achieve octave bandwidths and quantum-limited noise performance while approaching the dynamic range of conventional, low-noise cryogenic microwave amplifiers based on semiconductors. The successful realization of the TKIP amplifier would result in improved readout sensitivity for superconducting photon detectors, including microwave kinetic inductance detectors (MKIDs) and transition edge sensors (TESs). It would not only advance NASA’s mission in inflationary cosmology—the study of the earliest moments of the universe—but also its vision for mm-wave and x-ray astronomy. In the initial stages of the fellowship, I produced multiple models for simulating amplification in the TKIP. This included finite-difference time-domain, harmonic balance, and coupled-mode models, which provided detailed insight into amplifier nonlinearities and their effect on gain performance. I also produced models for understanding noise performance in the TKIP, motivated by the observed on-chip heating and its correlation with excess noise above the quantum limit. These models were consistent with the observation that the noise increases with frequency, as would be expected in a chip operating at considerably higher temperature than its environment. The models informed the development of a lumped-element parametric amplifier with intrinsic 50-ohm impedance, matching the external microwave environment. This amplifier achieves the same gain (~15 dB with 3 GHz 3 dB bandwidth) as previous distributed-element TKIPs based on coplanar waveguide, but with a factor of three lower pump power. The lower power mitigates on-chip heating and excess noise. Additionally, the physical length of the amplifier is a factor of ten lower than its distributed counterpart, resulting in significantly improved fabrication yield. We observe reflections at the input/output of the device, likely from wirebonds. These reflections result in standing waves and gain inefficiencies, meaning additional pump power is required to achieve some pre-determined gain level. With improvements to the signal launches and more generally, to the microwave environment, the TKIP should operate more robustly and efficiently and achieve high gain-bandwidth, large dynamic range, and quantum-limited noise performance.