A direct-current pumped Josephson travelling-wave amplifier

Claudio Guarcello, C. Barone, Giovanni Carapella +4 more

Hampus Renberg Nilsson

In order to build a large-scale quantum computer, one of the requirements is high-fidelity multiplexed qubit readout, which in turn relies on the use of ultralow-noise amplifiers. While Josephson Parametric Amplifiers (JPAs), using a cavity with few Josephson junctions, have shown promising results for single qubit readout, they have limitations such as low saturation power and a gain-bandwidth product restriction. This makes them less suited for frequency multiplexed qubit readout. A current-pumped Josephson Travelling-Wave Parametric Amplifier (JTWPA), using 4-wave mixing in a lumped-element transmission line, features both high saturation power as well as no restriction on large bandwidth and high gain. This is possible due to multiple junctions and the lack of a cavity. However, also this current pumped JTWPA has an inherent problem, namely phase mismatch between the pump and the signal. This prevents exponential gain. In this thesis, a current pumped JTWPA using the resonant phase matching (RPM) technique to reduce the phase mismatch problem is studied and characterised. The JTWPA shows high gain, high saturation power and a large signal-to-noise ratio improvement. The JTWPA is also used for qubit readout, for which it clearly improves the readout fidelity.

D. H. Slichter, Lafe Spietz, Ofer Naaman +2 more

Michael A. Tarasov, Aleksandra A. Gunbina, S. A. Lemzyakov +6 more

Abstract Prototypes of the design of Josephson traveling-wave parametric amplifier based on aluminum superconductor–insulator–superconductor junctions in the form of direct-current SQUIDs included in central conductor of coplanar line are developed, fabricated, and investigated. Three manufacturing methods for the fabrication of such devices are tested: two of them using shadow evaporation and one using magnetron sputtering and direct electron-beam lithography. Current–voltage characteristics of the junctions are measured at 0.3 K. A cryogenic setup for the measurement of spectral characteristics of such amplifier containing cold semiconductor amplifier with circulator and cooled attenuators of the channels of input signal and pump is developed. The absorption spectrum of coplanar directional coupler with a quarter-wave resonator dedicated for measurements of short chains from one to 27 SQUIDs is measured.

Claudio Guarcello, C. Barone, Giovanni Carapella +3 more

A comprehensive numerical analysis of the dynamical response of Josephson Traveling Wave Parametric Amplifiers (JTWPA) under varying driving conditions is presented. The primary goal is to examine the effects of a current–phase relation (CPR) incorporating a second-harmonic contribution. The analysis further investigates how parameters such as pump intensity, signal frequency, and DC bias current influence the transition to chaos. The results reveal a wide range of dynamical regimes in JTWPAs, offering insights into optimizing device performance and stability. Notably, the shape of the CPR is shown to have a significant impact on the operational effectiveness and stability of JTWPAs. To obtain results closer to real devices, numerical modeling of JTWPAs implementing Resonant Phase Matching (RPM) circuitry has been performed. We have verified that the introduction of RPM allows a significant increase in the amplifier gain also in the case of non-sinusoidal CPR. These findings may have important implications for the development of next-generation JTWPAs, which are essential components in quantum computing and precision measurement applications.