Superconducting circuits incorporating Josephson elements represent a promising hardware platform for quantum technologies. Potential applications include scalable quantum computing, microwave quantum networks, and quantum-limited amplifiers. However, progress in Josephson junction–based quantum technologies is facing the ongoing challenge of minimizing loss channels. This is also true for parametric superconducting devices based on nonlinear Josephson resonators. In this work, we report on the fabrication and characterization of low-loss Josephson parametric devices operated in the GHz frequency range, showing record internal quality factors. Specifically, we achieve internal quality factors Q int significantly exceeding 10 5 for both Josephson parametric converters and Josephson parametric amplifiers in the single-photon regime by fitting the scattering data. We confirm the extracted Q int values by analyzing purity of squeezed vacuum states generated by these devices. These low-loss devices mark a significant step forward in realizing high-performance quantum circuits, enabling further advancements in superconducting quantum technologies.Superconducting circuits incorporating Josephson elements represent a promising hardware platform for quantum technologies. Potential applications include scalable quantum computing, microwave quantum networks, and quantum-limited amplifiers. However, progress in Josephson junction–based quantum technologies is facing the ongoing challenge of minimizing loss channels. This is also true for parametric superconducting devices based on nonlinear Josephson resonators. In this work, we report on the fabrication and characterization of low-loss Josephson parametric devices operated in the GHz frequency range, showing record internal quality factors. Specifically, we achieve internal quality factors Q int significantly exceeding 10 5 for both Josephson parametric converters and Josephson parametric amplifiers in the single-photon regime by fitting the scattering data. We confirm the extracted Q int values by analyzing purity of squeezed vacuum states generated by these devices. These low-loss devices mark a significant step forward in realizing high-performance quantum circuits, enabling further advancements in superconducting quantum technologies.

arXiv:2412.11280Physical review. B./Physical review. BJun 5, 20253 citations

A simple method to fabricate Josephson junctions

Imran Mahboob, Satoshi Sasaki, Takaaki Takenaka

A minimal method to fabricate Al/AlO $_x$ /Al Josephson junctions (JJs) using photolithography and argon etching, before metallization and oxidation, is demonstrated. JJs with areas ranging from 1 to 6 $μ$ m $^2$ can be fabricated and, with the appropriate oxidation conditions, the junction resistance can be varied by $\sim$2 orders of magnitude. Transmission electron microscopy reveals the successful fabrication of JJs with few grain boundaries suggesting reduced energy loss from two-level-systems. Superconducting QUantum Interference Devices (SQUIDs) fabricated from this methodology exhibit reduced resistance variation over multiple chips, compared with electron beam lithography, and the devices can sustain repeated thermal cycles to 10 mK with the excellent flux response remaining unchanged. The quantum applications of this technology are demonstrated by embedding a SQUID resonator into a 3D cavity and parametrically amplifying low photon numbers with gains of $\sim$40 dB. This work establishes the simplest approach to fabricating JJs to date, and it could prove pivotal to the widespread utilization of superconducting circuit-based quantum technologies.A minimal method to fabricate Al/AlO$_x$/Al Josephson junctions (JJs) using photolithography and argon etching, before metallization and oxidation, is demonstrated. JJs with areas ranging from 1 to 6 $μ$m$^2$ can be fabricated and, with the appropriate oxidation conditions, the junction resistance can be varied by $\sim$2 orders of magnitude. Transmission electron microscopy reveals the successful fabrication of JJs with few grain boundaries suggesting reduced energy loss from two-level-systems. Superconducting QUantum Interference Devices (SQUIDs) fabricated from this methodology exhibit reduced resistance variation over multiple chips, compared with electron beam lithography, and the devices can sustain repeated thermal cycles to 10 mK with the excellent flux response remaining unchanged. The quantum applications of this technology are demonstrated by embedding a SQUID resonator into a 3D cavity and parametrically amplifying low photon numbers with gains of $\sim$40 dB. This work establishes the simplest approach to fabricating JJs to date, and it could prove pivotal to the widespread utilization of superconducting circuit-based quantum technologies.

quant-pharXiv:2604.25195Apr 29, 20260 citations

Optimization of materials for Josephson parametric amplifiers

Slawomir Simbierowicz

Dec 13, 20160 citations

Josephson traveling-wave parametric amplifier based on a low-intrinsic-loss lumped-element coplanar waveguide

C. W. Sandbo Chang, Arjan F. van Loo, Chih-Chiao Hung +4 more

Josephson traveling-wave parametric amplifiers (JTWPAs) are key to fast, frequency-multiplexed measurements in superconducting circuits. JTWPAs with periodic modulation are attractive, as they phase match without flux or dc bias, but they often suffer from significant gain ripples. Another common limitation in JTWPAs is intrinsic loss, which has prevented them from reaching the quantum limit of added noise. Here researchers address both issues by implementing an all-aluminum coplanar lumped-element JTWPA, using a qubit-compatible fabrication recipe. Their modulated device suppresses gain ripples for smooth, bias-free amplification, and approaches the quantum limit of added noise.Josephson traveling-wave parametric amplifiers (JTWPAs) are key to fast, frequency-multiplexed measurements in superconducting circuits. JTWPAs with periodic modulation are attractive, as they phase match without flux or dc bias, but they often suffer from significant gain ripples. Another common limitation in JTWPAs is intrinsic loss, which has prevented them from reaching the quantum limit of added noise. Here researchers address both issues by implementing an all-aluminum coplanar lumped-element JTWPA, using a qubit-compatible fabrication recipe. Their modulated device suppresses gain ripples for smooth, bias-free amplification, and approaches the quantum limit of added noise.

arXiv:2503.07559Physical Review AppliedSep 23, 20258 citations

A minimal method to fabricate Al/AlO

_x

/Al Josephson junctions (JJs) using photolithography and argon etching, before metallization and oxidation, is demonstrated. JJs with areas ranging from 1 to 6

μ

^2

can be fabricated and, with the appropriate oxidation conditions, the junction resistance can be varied by $\sim$2 orders of magnitude. Transmission electron microscopy reveals the successful fabrication of JJs with few grain boundaries suggesting reduced energy loss from two-level-systems. Superconducting QUantum Interference Devices (SQUIDs) fabricated from this methodology exhibit reduced resistance variation over multiple chips, compared with electron beam lithography, and the devices can sustain repeated thermal cycles to 10 mK with the excellent flux response remaining unchanged. The quantum applications of this technology are demonstrated by embedding a SQUID resonator into a 3D cavity and parametrically amplifying low photon numbers with gains of $\sim$40 dB. This work establishes the simplest approach to fabricating JJs to date, and it could prove pivotal to the widespread utilization of superconducting circuit-based quantum technologies.