An easily-prepared impedance matched Josephson parametric amplifier*

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.

Vacuum-gap-based lumped element Josephson parametric amplifier

“…To lower impedance mismatch at the signal reflection interface, impedance transformers becomes a common choice, among which, coplanar waveguide (CPW) based one is a primary candidate for its simple designable structure. [26][27][28][29] Commonly used CPWbased impedance transformers are composed of a quarterwavelength CPW section (with main characteristic parameters including resonant frequency ω q and impedance Z q ) and a half-wavelength CPW section (with ω h and Z h ). According to transmission line theory, input impedance of a load can be transformed via CPW section, which can be expressed as Z in (ω s ) = Z cpw {Z L + iZ cpw tan(2π νω s /ω cpw )}/{Z cpw + iZ L tan(2π νω s /ω cpw )}.…”