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Chinese Physics B

An easily-prepared impedance matched Josephson parametric amplifier*

Yapeng Lu, Quan Zuo, Jiazheng Pan, Junliang Jiang, Xingyu Wei, Zishuo Li, Wenqu Xu, Kaixuan Zhang, Tingting Guo, Shuo Wang, Chunhai Cao, Weiwei Xu, Guozhu Sun, Peiheng Wu

Published May 24, 2021• 6 citations
Publisher

Abstract

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.

DOI
10.1088/1674-1056/ac0420

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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.
We propose and realize a multi-resonator coupled impedance-matched Josephson parametric amplifier. Parallel plate capacitors serve as couplers to achieve coupling between the nonlinear resonator containing the Josephson loop and the half-wavelength resonator, and between the half-wavelength resonators themselves. By precisely designing each coupling strength, we effectively extend the amplifier's bandwidth. Through a combination of circuit-level and electromagnetic field simulations, we optimize the structural parameters of the resonators and capacitors. The two measured devices have 15 dB gain with a bandwidth of 1.3 GHz and 20 dB gain with a bandwidth of 1.1 GHz, respectively, with near-quantum-limited noise temperatures.
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.
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.
We present a fishbone-like lumped-element artificial transmission line to overcome impedance mismatch in a reflection-type Josephson parametric amplifier between a nonlinear resonator and an external transmission line. Using this easily prepared architecture, we design and fabricate a broadband Josephson parametric amplifier, which has gain in an excess of 20 dB with a bandwidth of hundreds of MHz. Furthermore, by varying the working point of the device, the operating frequency of amplification can be tuned in a wide frequency range of 1 GHz while the amplifier operates in the mode of either three-wave mixing or four-wave mixing. Such a parametric amplifier is suitable for engineering applications of superconducting circuit quantum electrodynamics.
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.
We designed and fabricated an impedance-matched Josephson parametric amplifier (JPA) working in the flux-pump mode for the broadband amplification of microwave signals. A simple fabrication method suitable for a small cleanroom was developed. We also studied the phase response, as well as the gain, as a function of signal frequency and pump power at various pump frequencies. The phase response can be explained with the behavior of the nonlinear Duffing oscillator. The observed decrease of the resonance frequency as the pump power increases, as well as the emergence of an unstable bifurcation zone, are the characteristic nonlinear behavior of the Duffing oscillator. The features of the gain profile in the stable zone can be explained with a model adapted from the theoretical model for the two-dimensional gain profile of an impedance-matched, current-pumped JPA. Over 17 dB gain with a bandwidth more than 300 MHz (centered around 6.45 GHz) was observed. Our impedance-matched JPA is used for improving the fast readout fidelity of transmon qubits.