Broadband kinetic inductance parametric amplifiers with impedance engineering

Broadband quantum-limited parametric amplifiers (PAs) are essential components in quantum information science and technology. Impedance-engineered resonator-based PAs and traveling-wave PAs are the primary approaches taken to overcome the gain-bandwidth constraint. While the former PAs are simpler to fabricate, the target characteristic impedance ${Z}_{\mathrm{NR}}$ of the nonlinear resonator has been restricted to be below $10\phantom{\rule{0.2em}{0ex}}\mathrm{\ensuremath{\Omega}}$, requiring large capacitance. Moreover, these PAs have only been implemented with aluminum-based Josephson junctions (JJs), hindering their operation at high temperatures or strong magnetic fields. To address these issues, we propose a three-stage impedance-transformer scheme, showcased with a 20 nm thick, 250 nm wide, high-kinetic-inductance niobium-titanium-nitride ($\mathrm{Nb}\mathrm{Ti}\mathrm{N}$) film. Our scheme enables ${Z}_{\mathrm{NR}}$ up to several tens of ohms---a tenfold improvement over conventional designs, achieved through an additional quarter-wavelength transmission line with a characteristic impedance of 180 $\mathrm{\ensuremath{\Omega}}$. Our kinetic-inductance impedance-engineered parametric amplifiers (KIMPAs), featuring a 330 fF shunt capacitor, demonstrate a phase-preserving amplification with a 450-MHz bandwidth at 17 dB gain, and added noise ranging from 0.5 to 1.3 quanta near the center frequency of 8.4 GHz. Owing to the high critical current of the $\mathrm{Nb}\mathrm{Ti}\mathrm{N}$ nanowire, the KIMPA also achieves an output saturation power of up to $\ensuremath{-}51\ifmmode\pm\else\textpm\fi{}3$ dBm, approximately 25 dB higher than that of JJ-based PAs. This scheme also opens new possibilities for other three-wave-mixing building blocks.