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arXiv:2403.11354 · Journal of Low Temperature Physics

Kinetic Inductance Traveling Wave Amplifier Designs for Practical Microwave Readout Applications

Andrea Giachero, Michael R. Vissers, Jordan Wheeler, Logan A. Howe, J. Gao, Jason E. Austermann, Johannes Hubmayr, Angelo Nucciotti, Joel N. Ullom

Published Apr 5, 2024• 15 citations
arXivHTMLPDF

Abstract

Abstract A Kinetic Inductance Traveling Wave Amplifier (KIT) utilizes the nonlinear kinetic inductance of superconducting films, particularly niobium titanium nitride (NbTiN), for parametric amplification. These amplifiers achieve remarkable performance in terms of gain, bandwidth, and compression power and frequently approach the quantum limit for noise. However, most KIT demonstrations have been isolated from practical device readout systems. Using a KIT as the first amplifier in the readout chain of an unoptimized microwave SQUID multiplexer coupled to a transition-edge sensor microcalorimeter, we see an initial improvement in the flux noise [1]. One challenge in KIT integration is the considerable microwave pump power required to drive the non-linearity. To address this, we have initiated efforts to reduce the pump power by using thinner NbTiN films and an inverted microstrip transmission line design. In this article, we present the new transmission line design, fabrication procedure, and initial device characterization—including gain and added noise. These devices exhibit over 10 dB of gain with a 3 dB bandwidth of approximately 5.5–7.25 GHz, a maximum practical gain of 12 dB, and typical gain ripple under 4 dB peak to peak. We observe an appreciable impedance mismatch in the NbTiN transmission line, which is likely the source of the majority of the gain ripple. Finally, we perform an initial noise characterization and demonstrate system-added noise of three quanta or less over nearly the entire 3 dB bandwidth.

DOI
10.1007/s10909-024-03078-1

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Kinetic inductance traveling-wave parametric amplifiers (KITs) are under development for the read out of large cryogenic detector arrays. We present new KIT designs based on 20nm NbTiN films patterned by use of standard optical photolithography. We report device gain, bandwidth, and noise properties, which approach the quantum limit. In addition, we demonstrate a KIT preamplifier with a microwave SQUID multiplexer. The improved input referred current noise, as compared to standard HEMT readout, opens up new possibilities for cryogenic receivers. We discuss these benefits.

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We present a theoretical model and experimental characterization of a microwave kinetic inductance traveling-wave (KIT) amplifier, whose noise performance, measured by a shot-noise tunnel junction (SNTJ), approaches the quantum limit.Biased with a dc current, this amplifier operates in a three-wave mixing fashion, thereby reducing by several orders of magnitude the power of the microwave pump tone and associated parasitic heating compared to conventional four-wave mixing KIT amplifier devices.It consists of a 50 artificial transmission line whose dispersion allows for a controlled amplification bandwidth.We measure 16.5 +1 -1.3 dB of gain across a 2 GHz bandwidth with an input 1 dB compression power of -63 dBm, in qualitative agreement with theory.Using a theoretical framework that accounts for the SNTJgenerated noise entering both the signal and idler ports of the KIT amplifier, we measure the system-added noise of an amplification chain that integrates the KIT amplifier as the first amplifier.This system-added noise, 3.1 ± 0.6 quanta (equivalent to 0.66 ± 0.15 K) between 3.5 and 5.5 GHz, is the one that a device replacing the SNTJ in that chain would see.This KIT amplifier is therefore suitable to read large arrays of microwave kinetic inductance detectors and promising for multiplexed superconducting qubit readout.

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Quantum computing systems and fundamental physics experiments using superconducting technologies frequently require signal amplification chains operating near the quantum limit of added noise. Both Josephson parametric amplifiers (JPAs) and traveling wave parametric amplifiers (TWPAs) have been used as first-stage amplifiers to enable readout chains operating within a few quanta or less of the quantum limit. These devices are also presently entering the commercial industry. However, nearly all demonstrations and existing products require bulky external microwave components for interconnection and application of requisite biases. These components – cabling interconnects, bias tees, directional couplers, and diplexers – increase the overall amplifier footprint, installation complexity, and reduce already limited available cryogenic volumes. Additionally, these components introduce loss and reflections which impact the measurement efficiency and readout system noise performance; thus making it more difficult to operate near the quantum limit. Here we present the design and validation of microfabricated bias tees and directional couplers for operating three-wave mixing kinetic inductance TWPAs (KITs). We report the performance of KITs integrated with the microfabricated rf components. Using these devices we demonstrate reduction in the amplifier installation footprint by a factor of nearly five and elimination of all external, lossy microwave components previously required to operate a KIT. Our device displays a 2.8 GHz 3 dB bandwidth with a median true gain of 17.5 dB and median system noise of 3.4 quanta. These efforts represent the first full integration of all rf components mandatory for TWPA operation on-chip. Our results mark significant progress towards the miniaturization and simplification of parametric amplifier setups and will aid in their more widespread applicability.

arXiv:2503.03608•IEEE Transactions on Applied Superconductivity•Mar 21, 2025•8 citations
Abstract A Kinetic Inductance Traveling Wave Amplifier (KIT) utilizes the nonlinear kinetic inductance of superconducting films, particularly niobium titanium nitride (NbTiN), for parametric amplification. These amplifiers achieve remarkable performance in terms of gain, bandwidth, and compression power and frequently approach the quantum limit for noise. However, most KIT demonstrations have been isolated from practical device readout systems. Using a KIT as the first amplifier in the readout chain of an unoptimized microwave SQUID multiplexer coupled to a transition-edge sensor microcalorimeter, we see an initial improvement in the flux noise [1]. One challenge in KIT integration is the considerable microwave pump power required to drive the non-linearity. To address this, we have initiated efforts to reduce the pump power by using thinner NbTiN films and an inverted microstrip transmission line design. In this article, we present the new transmission line design, fabrication procedure, and initial device characterization—including gain and added noise. These devices exhibit over 10 dB of gain with a 3 dB bandwidth of approximately 5.5–7.25 GHz, a maximum practical gain of 12 dB, and typical gain ripple under 4 dB peak to peak. We observe an appreciable impedance mismatch in the NbTiN transmission line, which is likely the source of the majority of the gain ripple. Finally, we perform an initial noise characterization and demonstrate system-added noise of three quanta or less over nearly the entire 3 dB bandwidth.
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.
Kinetic inductance traveling-wave parametric amplifiers (KITs) are under development for the read out of large cryogenic detector arrays. We present new KIT designs based on 20nm NbTiN films patterned by use of standard optical photolithography. We report device gain, bandwidth, and noise properties, which approach the quantum limit. In addition, we demonstrate a KIT preamplifier with a microwave SQUID multiplexer. The improved input referred current noise, as compared to standard HEMT readout, opens up new possibilities for cryogenic receivers. We discuss these benefits.
Kinetic inductance traveling-wave parametric amplifiers (KI-TWPAs) have a wide instantaneous bandwidth with a near quantum-limited noise performance and a relatively high dynamic range. Because of this, they are suitable readout devices for cryogenic detectors and superconducting qubits and have a variety of applications in quantum sensing. This work discusses the design, fabrication, and performance of a KI-TWPA based on four-wave mixing in a NbTiN microstrip transmission line. This device amplifies a signal band from 4 to 8 GHz without contamination from image tones, which are produced in a separate higher frequency band. The 4–8 GHz band is commonly used to read out cryogenic detectors, such as microwave kinetic inductance detectors and Josephson junction-based qubits. We report a measured maximum gain of over 20 dB using four-wave mixing with a 1 dB gain compression point of −58 dBm at 15 dB of gain over that band. The bandwidth and peak gain are tunable by adjusting the pump-tone frequency and power. Using a Y-factor method, we measure an amplifier-added noise of 0.5 ≤ Nadded ≤ 1.5 photons from 4.5 to 8 GHz.
We present a theoretical model and experimental characterization of a microwave kinetic inductance traveling-wave (KIT) amplifier, whose noise performance, measured by a shot-noise tunnel junction (SNTJ), approaches the quantum limit.Biased with a dc current, this amplifier operates in a three-wave mixing fashion, thereby reducing by several orders of magnitude the power of the microwave pump tone and associated parasitic heating compared to conventional four-wave mixing KIT amplifier devices.It consists of a 50 artificial transmission line whose dispersion allows for a controlled amplification bandwidth.We measure 16.5 +1 -1.3 dB of gain across a 2 GHz bandwidth with an input 1 dB compression power of -63 dBm, in qualitative agreement with theory.Using a theoretical framework that accounts for the SNTJgenerated noise entering both the signal and idler ports of the KIT amplifier, we measure the system-added noise of an amplification chain that integrates the KIT amplifier as the first amplifier.This system-added noise, 3.1 ± 0.6 quanta (equivalent to 0.66 ± 0.15 K) between 3.5 and 5.5 GHz, is the one that a device replacing the SNTJ in that chain would see.This KIT amplifier is therefore suitable to read large arrays of microwave kinetic inductance detectors and promising for multiplexed superconducting qubit readout.
Background Kinetic inductance travelling-wave parametric amplifiers (KITWPAs) have proven effective in achieving high gain over broad bandwidths whilst achieving near quantum-limited noise performance, properties which are extremely important for many ultra-sensitive experiments such as radio/millimetre/sub-millimetre astronomy, neutrino mass experiments, and axion dark matter searches, as well as commercial applications like quantum computational and communication systems. Methods This paper introduces the preliminary experimental exploration of an alternative KITWPA utilising thin titanium nitride (TiN) films as opposed to the conventionally used niobium titanium nitride (NbTiN) films. TiN films exhibit properties that could be advantageous for KITWPA operation, owing to its controllable critical temperature (T c) and physical robustness, hence KITWPAs fabricated from TiN films have the potential to replace NbTiN-based TWPAs for various applications, such as reducing the high pump power required to drive a NbTiN TWPA. Our TiN-based KITWPA devices were designed and fabricated with a 42 cm long coplanar waveguide transmission line patterned into a 100 nm thick TiN film, wound in a double spiral fashion to fit into a 2.2×2.2 cm chip. Results We successfully achieved broadband performance, with the best device displaying a peak averaged gain of ~5 dB with a bandwidth of ~3–13 GHz, making this one of the first broadband gain measurements of a TiN KITWPA reported in the literature. Despite this, the measured gain in all batches was lower than simulated due unexpected additional loss mechanisms. Conclusions The preliminary results presented here suggest that TiN films are suitable for KITWPA operation, although further investigation is required to improve the gain performance.
Quantum computing systems and fundamental physics experiments using superconducting technologies frequently require signal amplification chains operating near the quantum limit of added noise. Both Josephson parametric amplifiers (JPAs) and traveling wave parametric amplifiers (TWPAs) have been used as first-stage amplifiers to enable readout chains operating within a few quanta or less of the quantum limit. These devices are also presently entering the commercial industry. However, nearly all demonstrations and existing products require bulky external microwave components for interconnection and application of requisite biases. These components – cabling interconnects, bias tees, directional couplers, and diplexers – increase the overall amplifier footprint, installation complexity, and reduce already limited available cryogenic volumes. Additionally, these components introduce loss and reflections which impact the measurement efficiency and readout system noise performance; thus making it more difficult to operate near the quantum limit. Here we present the design and validation of microfabricated bias tees and directional couplers for operating three-wave mixing kinetic inductance TWPAs (KITs). We report the performance of KITs integrated with the microfabricated rf components. Using these devices we demonstrate reduction in the amplifier installation footprint by a factor of nearly five and elimination of all external, lossy microwave components previously required to operate a KIT. Our device displays a 2.8 GHz 3 dB bandwidth with a median true gain of 17.5 dB and median system noise of 3.4 quanta. These efforts represent the first full integration of all rf components mandatory for TWPA operation on-chip. Our results mark significant progress towards the miniaturization and simplification of parametric amplifier setups and will aid in their more widespread applicability.