Investigating the χ(3) nonlinearity of a Josephson junction array for travelling-wave parametric amplification in the W-band

Journal article

At microwave frequencies, Josephson junction arrays have been widely employed to create metamaterials exhibiting a third-order χ⁽³⁾) nonlinearity, analogous to the Kerr effect in optics. These nonlinear metamaterials enable parametric amplification, as in Josephson travelling-wave parametric amplifiers (JTWPAs), which achieve quantum-limited noise performance over multigigahertz bandwidths. The exceptional properties of JTWPAs make them ideal for the sensitive readout of weak microwave signals, with applications in quantum computing, astrophysics, and fundamental physics experiments. Extending JTWPAs to higher frequencies, such as the W-band (70–110 GHz), holds promise for first-stage amplification in astronomical receivers, lowering system noise; as well as for reading out emerging superconducting qubit architectures at these frequencies. In this work, we investigate the χ⁽³⁾ nonlinear properties of Josephson arrays operating in the W-band as a step toward realizing parametric gain at these frequencies. We designed and fabricated an array composed of 704 Nb/Al-AlO_x/Nb tunnel junctions and experimentally demonstrated four-wave mixing via idler tone generation, providing clear evidence of third-order nonlinearity. These results mark an important step toward novel millimetre-wave and submillimetre-wave parametric-amplifier-based receiver technologies.

Authors: Navarro Montilla, J; Stephenson, RC; Barbier, A; Klimovich, N; Bortolotti, Y

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IEEE
• Journal: IEEE Transactions on Applied Superconductivity
• Volume: 36
• Issue: 1
• Article number: 3500111
• Publication date: 2025-11-24
• Acceptance date: 2025-11-17
• DOI: 10.1109/tasc.2025.3636612
• EISSN: 1558-2515
• ISSN: 1051-8223
• Language: English
• Keywords: junctions; Josephson junctions; inductance; microwave amplifiers; cutoff frequency; superconducting transmission lines; superconducting microwave devices; capacitance; qubit; microwave imaging