Magnetic field dependence of a Josephson traveling-wave parametric amplifier and integration into a high-field setup

Abstract

We investigate the effect of the magnetic field on a photonic crystal Josephson traveling-wave parametric amplifier (TWPA). We show that the observed change in the photonic band gap and plasma frequency of the TWPA can be modeled by considering the suppression of the critical current in the Josephson junctions (JJs) of the TWPA due to the Fraunhofer effect and closing of the superconducting gap. Accounting for the JJ geometry is crucial for understanding the field dependence. In one in-plane direction, the TWPA band gap can be shifted by 2 GHz using up to 60 mT of field, without losing gain or bandwidth, showing that TWPAs without superconducting quantum interference devices (SQUID) can be field tunable. In the other in-plane direction, the magnetic field is perpendicular to the larger side of the Josephson junctions, so the Fraunhofer effect has a smaller period. This larger side of the JJs is modulated to create the band gap. The field interacts more strongly with the larger junctions, and as a result, the TWPA band gap closes and reopens as the field increases, causing the TWPA to become severely compromised already at 2 mT. A slightly higher operating limit of 5 mT is found in the out-of-plane field, for which the TWPA’s response is hysteretic. These measurements reveal the requirements for magnetic shielding needed to use TWPAs in experiments where high fields at the sample are required. With magnetic shields and at a distance from a sample at the magnet center, we can operate the TWPA while applying over 2 T to the sample.

Source-reported materials — not catalogue approval

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