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arXiv:2503.06936 · AIP Advances

Fabrication and characterization of impedance-transformed Josephson parametric amplifier

Zheng-Yang Mei, Xiaohui Song, X. C. Guo, Xiang Li, Yun‐Hao Shi, Gui-Han Liang, Cheng-Lin Deng, Li Li, Yang He, Dongning Zheng, Kai Xu, Heng Fan, Zhongcheng Xiang

Published Jul 1, 2025• 1 citation
arXivHTMLPDF

Abstract

In this paper, we introduce a method of using a double-layer resist lift-off process to prepare the capacitor dielectric layer for fabricating impedance-engineered Josephson parametric amplifiers (IMPAs). Compared to prior art, this method enhances fabrication success rate and accelerates production. The IMPA we made, experimentally achieves an instantaneous bandwidth over 950 (600) MHz with a gain exceeding 10 (14) dB, along with saturation input power of −115 dBm and near quantum-limited noise. We demonstrate the negligible backaction from the IMPA on superconducting qubits, resulting in no significant degradation of the relaxation time and coherence time of the qubits. The IMPA improves the signal-to-noise ratio from 1.69 to 14.56 and enables the amplification chain to achieve high quantum efficiency with η ≈ 0.26, making it a critical necessity for large-scale quantum computation.

DOI
10.1063/5.0270099

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In this paper, we introduce a method of using a double-layer resist lift-off process to prepare the capacitor dielectric layer for fabricating impedance-engineered Josephson parametric amplifiers (IMPAs). Compared to prior art, this method enhances fabrication success rate and accelerates production. The IMPA we made, experimentally achieves an instantaneous bandwidth over 950 (600) MHz with a gain exceeding 10 (14) dB, along with saturation input power of −115 dBm and near quantum-limited noise. We demonstrate the negligible backaction from the IMPA on superconducting qubits, resulting in no significant degradation of the relaxation time and coherence time of the qubits. The IMPA improves the signal-to-noise ratio from 1.69 to 14.56 and enables the amplification chain to achieve high quantum efficiency with η ≈ 0.26, making it a critical necessity for large-scale quantum computation.
An impedance matched parametric amplifier (IMPA) with Josephson junctions is fabricated and characterized. A hybrid structure containing coplanar and strip structures is implemented to realize an impedance taper line and a plate capacitor in an LC nonlinear resonator based on Josephson junctions. The upper plate of the capacitor is isolated with SiN x without grounding as well as the strips. Such easily-prepared designs greatly reduce the requirements for lithography alignment and precision, which makes the fabrication process more reliable. The experimental results show that in such IMPA a gain higher than 25 dB with a bandwidth of about 100 MHz can be obtained. This broadband amplifier operates close to the quantum limit. By adjusting the working point, a higher bandwidth of about 400 MHz can be obtained with a gain of about 17 dB.
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We report the fabrication and characterization of an impedance matched Josephson parametric amplifier (IMPA). A multisection λ/4 transmission line transformer (TLT) is utilized, which can reduce the input impedance and provide a wide impedance matched bandwidth. In addition, the whole IMPA device is fabricated on a LaAlO3 substrate with a dielectric constant of 23.4, much larger compared to the commonly used intrinsic silicon substrate, to provide larger grounded capacitance, making the fabrication of the multisection λ/4 TLT more precise and reliable. The experimental results show that by adjusting the working point, the amplifier has a bandwidth of 580 MHz with a gain of more than 15 dB. The average input saturation power is about −115 dBm within the bandwidth. Additionally, its noise performance is close to the quantum-limited level.
Josephson parametric amplifiers (JPAs) with nearly quantum-limited noise performance have become indispensable devices for the measurements of superconducting quantum information. We have developed an all-Nb lumped-element flux-driven JPA operating in the three-wave mixing mode. Our Nb-based JPA comprises Nb/Al-AlO x /Nb Josephson junctions, a parallel-plate capacitor with SiO2 dielectric sandwiched between two Nb layers, a bottom coplanar waveguides layer, and a top Nb wiring layer. We experimentally demonstrate a 20 dB gain over a 190 MHz bandwidth, a mean 1 dB compression of –123 dBm, and near quantum-limited noise performance. This fabrication process can be further used to design impedance transformed parametric amplifiers for multiple-qubit readout.
We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a λ/2 transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of −110 dBm and near quantum-limited noise. The results are in a good agreement with our theoretical model.
We present an experimental demonstration of an impedance-engineered Josephson parametric amplifier (IEJPA) fabricated in a single-step lithography process. Impedance-engineering is implemented using a lumped-element series LC circuit. We use a simpler lithography process where the entire device—impedance transformer and Josephson parametric amplifier (JPA)—is patterned in a single electron beam lithography step, followed by a double-angle Dolan-bridge technique for Al–AlOx–Al deposition. We observe amplification with 18 dB gain over a wide 400 MHz bandwidth centered around 5.3 GHz with added noise approaching the quantum limit, and a saturation power of −114 dBm. To accurately explain our experimental results, we extend existing theories for IEJPAs to incorporate the full sine nonlinearity of both the JPA and the transformer. Our work provides a route to simpler realization of broadband JPAs and a theoretical foundation for a regime of JPA operation that has been less explored in literature.