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arXiv:2504.17145 · Physical Review Applied

Broadband kinetic inductance parametric amplifiers with impedance engineering

Chih-Chiao Hung, Hiroki Kutsuma, C. W. Sandbo Chang, Arjan F. van Loo, Yasunobu Nakamura

Published Nov 7, 2025• 1 citation
arXivHTMLPDF

Abstract

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.

DOI
10.1103/6xk3-tvpb

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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 ZNR{Z}_{\mathrm{NR}}ZNR​ of the nonlinear resonator has been restricted to be below 10\ensuremathΩ10\phantom{\rule{0.2em}{0ex}}\mathrm{\ensuremath{\Omega}}10\ensuremathΩ, 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 (NbTiN\mathrm{Nb}\mathrm{Ti}\mathrm{N}NbTiN) film. Our scheme enables ZNR{Z}_{\mathrm{NR}}ZNR​ 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 \ensuremathΩ\mathrm{\ensuremath{\Omega}}\ensuremathΩ. 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 NbTiN\mathrm{Nb}\mathrm{Ti}\mathrm{N}NbTiN nanowire, the KIMPA also achieves an output saturation power of up to \ensuremath−51\ifmmode±\else\textpm\fi3\ensuremath{-}51\ifmmode\pm\else\textpm\fi{}3\ensuremath−51\ifmmode±\else\textpm\fi3 dBm, approximately 25 dB higher than that of JJ-based PAs. This scheme also opens new possibilities for other three-wave-mixing building blocks.
We present a detailed simulation and design framework for realizing traveling wave parametric amplifiers (TWPAs) using the nonlinear kinetic inductance of disordered superconductors -- in our case niobium-titanium-nitride (NbTiN). These kinetic inductance TWPAs (KITs) operate via three-wave mixing (3WM) to achieve high broadband gain and near-quantum-limited (nQL) noise. Representative fabricated devices -- realized using an inverted microstrip (IMS), dispersion-engineered, artificial transmission line -- demonstrate power gains above 25 dB, bandwidths beyond 3 GHz, and achieve ultimate system noise levels of 1.1 quanta even when operated with no magnetic shielding. These performance metrics are competitive with state-of-the-art Josephson-junction-based TWPAs but involve simpler fabrication and able to providing three orders of magnitude higher dynamic range (IIP1=−68IIP_1 = -68IIP1​=−68 dBm, IIP3=−55IIP_3 = -55IIP3​=−55 dBm), and high magnetic field resilience -- making KITs an attractive technology for highly multiplexed readout of quantum information and superconducting detector systems.
Advancing superconducting quantum devices to higher operating frequencies broadens their functionality and enables operation at elevated temperatures, but it also requires near-quantum-limited amplifiers beyond the few-gigahertz regime. Here we present a junction-free, kinetic-inductance parametric amplifier based on thin-film niobium nitride (NbN) operating at 23 GHz in the microwave K-band, achieving a gain up to 40 dB, a 100 MHz gain-bandwidth product, a 1 dB saturation input power of -85 dBm with 23 dB gain, and added noise no greater than 1.4 quanta for phase-preserving amplification. Leveraging the large superconducting gap of NbN, this architecture can be extended to even higher frequencies, supporting applications such as high-fidelity readout of millimeter-wave superconducting qubits and axion searches over an expanded mass window.
Advancing superconducting quantum devices to higher operating frequencies broadens their functionality and enables operation at elevated temperatures, but it also requires near-quantum-limited amplifiers beyond the few-gigahertz regime. Here, we present a junction-free, kinetic-inductance parametric amplifier based on thin-film niobium nitride (NbN) operating at 23 GHz in the microwave K-band, achieving a gain up to 40 dB, a 100 MHz gain–bandwidth product, a 1 dB saturation input power of −85 dBm with 23 dB gain, and added noise not greater than 1.4 quanta for phase-preserving amplification. Leveraging the large superconducting gap of NbN, this architecture can be extended to even higher frequencies, supporting applications such as high-fidelity readout of millimeter-wave superconducting qubits and axion searches over an expanded mass window.
Microwave parametric amplifiers operating at the quantum noise limit have become indispensable tools for a range of cryogenic quantum technologies. These amplifiers are typically constructed from nonlinear Josephson junctions, which limit the ability to amplify high-power signals. This study reports a device based instead on the weakly nonlinear kinetic inductance intrinsic to a superconducting film of niobium titanium nitride. The amplifier offers large phase-sensitive gain and high power handling, plus a simple design and fabrication process. As it contains no junctions, it is robust to electrostatic discharge and potentially operable under high temperatures and large magnetic fields.
Parametric converters are parametric amplifiers that mix two spatially separate nondegenerate modes and are commonly used for amplifying and squeezing microwave signals in quantum computing and sensing. In Josephson parametric converters, the strong localized nonlinearity of the Josephson junction limits the amplification and squeezing, as well as the dynamic range, in current devices. In contrast, a weak distributed nonlinearity can provide higher gain and dynamic range, when implemented as a kinetic inductance (KI) nanowire of a dirty superconductor, and has additional benefits such as resilience to magnetic field, higher-temperature operation, and simplified fabrication. Here, we propose, demonstrate, and analyze the performance of a KI parametric converter that relies on the weak distributed nonlinearity of a Nb-Ti-N KI nanowire. The device utilizes three-wave mixing induced by a dc current bias. We demonstrate its operation as a nondegenerate parametric amplifier with high phase-sensitive gain, reaching two-mode amplification and deamplification of approximately 30 dB for two resonances separated by 0.8 GHz, in excellent agreement with our theory of the device. We observe a dynamic range of $\ensuremath{-}108$ dBm at 30 dB gain. Our device can significantly broaden applications of quantum-limited signal processing devices including phase-preserving amplification and two-mode squeezing.
Parametric amplification is essential for quantum measurement, enabling the amplification of weak microwave signals with minimal added noise. While Josephson-junction-based amplifiers have become standard in superconducting quantum circuits, their magnetic sensitivity, limited saturation power, and sub-kelvin operating requirements motivate the development of alternative nonlinear platforms. Here we demonstrate a two-mode kinetic-inductance parametric amplifier based on a pair of capacitively coupled Kerr-nonlinear resonators fabricated from NbTiN and NbN thin films. The distributed Kerr nonlinearity of these materials enables nondegenerate four-wave-mixing amplification with gains approaching 40 dB, gain-bandwidth products up to 6.9 MHz, and 1-dB compression powers two to three orders of magnitude higher than those of state-of-the-art Josephson amplifiers. A coupled-mode theoretical model accurately captures the pump-induced modification of the hybridized modes and quantitatively reproduces the observed signal and idler responses. The NbN device exhibits a significantly larger Kerr coefficient and superior gain-bandwidth performance, highlighting the advantages of high-kinetic-inductance materials. Our results establish coupled kinetic-inductance resonators as a robust platform for broadband, high-power, and magnetically resilient quantum-limited amplification, offering a scalable route for advanced readout in superconducting qubits, spin ensembles, quantum dots, and other microwave-quantum technologies.