We present a Josephson traveling-wave parametric amplifier (JTWPA) based on a low-loss coplanar lumped-element waveguide architecture. By employing open-stub capacitors and Manhattan-pattern junctions, our device achieves an insertion loss below 1~dB up to 12~GHz. We introduce windowed sinusoidal modulation for phase matching, demonstrating that a smooth transition in the impedance-modulation strength effectively suppresses intrinsic gain ripples. Using Tukey-windowed modulation with 8\% impedance variation, we achieve 20\text{--}23-dB~gain over 5-GHz bandwidth under ideal matching conditions. In a more practical circuit having impedance mismatches, the device maintains 17\text{--}20-dB gain over 4.8-GHz bandwidth with an added noise of 0.18~quanta above standard quantum limit at 20-dB gain and −99-dBm saturation power, while featuring zero to negative backward gain below the band-gap frequency.
@article{arxiv.2503.07559,
title = {Josephson traveling-wave parametric amplifier based on low-intrinsic-loss coplanar lumped-element waveguide},
author = {C. W. Sandbo Chang and Arjan F. Van Loo and Chih-Chiao Hung and Yu Zhou and Christian Gnandt and Shuhei Tamate and Yasunobu Nakamura},
journal= {arXiv preprint arXiv:2503.07559},
year = {2025}
}