研究目的
To engineer the nonlinearity of a SNAIL parametric amplifier (SPA) over multiple orders of magnitude by varying its physical design, and to systematically explore and minimize the phenomena of gain compression and intermodulation distortion to achieve higher saturation power without sacrificing other desirable characteristics.
研究成果
The SPA, a three-wave-mixing degenerate parametric amplifier, was optimized to achieve 1-dB compression powers on par with the best reported values for resonant quantum-limited parametric amplifiers, over the entire tunable bandwidth of 1 GHz of the device, without sacrificing any other desirable characteristics. The fourth-order Kerr term in the amplifier Hamiltonian was confirmed as the primary cause of gain compression and intermodulation distortion.
研究不足
The study is limited by the practical difficulty in realizing microstrip embedding structures with impedances significantly different from 50 Ω, and by the parasitic geometric inductances in the leads used to make the junctions, which prevent the reduction of LJ much below its current value of approximately 40 pH without significantly affecting the participation ratio p.
1：Experimental Design and Method Selection:
The SPA is realized by placing an array of SNAILs at the center of a λ/2 section of microstrip transmission line. The nonlinearity is engineered by varying the physical design parameters such as the number of SNAILs (M), the junction inductance ratio (α), and the Josephson inductance (LJ).
2：Sample Selection and Data Sources:
Five devices with varying parameters (LJ, M, α, Cc, ω0) were measured in the experiment. The resonant frequency ωa and coupling to the transmission line κ were extracted from resonance fits at each flux point.
3：List of Experimental Equipment and Materials:
The devices were fabricated using a Dolan bridge process for aluminum (Al) on silicon (Si). The microstrip transmission-line sections were formed by a 2-μm-thick silver (Ag) layer deposited on the back of a 300-μm-thick Si wafer.
4：Experimental Procedures and Operational Workflow:
The experimental characterization was performed in a helium-dilution refrigerator with a standard microwave reflection measurement setup. A magnet coil applied a magnetic flux to each SNAIL, and measurements were performed with a PNA-X network analyzer.
5：Data Analysis Methods:
The nonlinearities g3 and g4 were extracted from gain and Stark shift measurements, respectively. The saturation power and intermodulation distortion were characterized and compared with first-principles theory.
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