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.

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.

Superconducting quantum computing is currently one of the most promising platforms for universal quantum information processing. The readout resonator is an essential integral part of a superconducting qubit, while its size is much larger compared to the Josephson junction. We propose and realize a new readout resonator using space-filling curves, specifically Hilbert space-filling curves. We introduce the frequency analysis method and demonstrate a qubit sample, in which the Hilbert-space-filling-curves resonator (HSFCR) is used to read out the qubit states. We also propose to fabricate the HSFCRs and Josephson junctions simultaneously in the same processes of E-beam lithography and E-beam evaporation. Our design reduces the resonator area sufficiently and, thus, will help to improve the integration of superconducting qubits, as well as to design other superconducting quantum devices.