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arXiv:2610.29901

Superconducting parametric amplifiers based on arrays of unequal Josephson junction elements

Boris Chesca, Tom Dixon, Narendra Acharya, Renuka D. Pothuraju, Jacob W. Dunstan, Connor D. Shelly, Oscar W. Kennedy

quant-phphysics.app-phSubmitted Oct 21, 2026• Announced Oct 22, 2026• 0 citations
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Abstract

Impedance matching is a crucial feature of an amplifier used to increase its instantaneous bandwidth and is typically achieved using static LC resonators. Here we show an approach to impedance matching in parametric amplifiers using arrays of unequal Josephson-junction-based elements (rf/dc SQUIDs, SNAILs, etc). The elements act either as small-footprint flux-tunable inductors forming an impedance-matching circuit, or 'active' amplifier elements which result in amplifier gain. We develop an analytical theory describing these systems, predicting a quasi-non-periodic amplifier frequency and gain modulation with applied flux and the broadening of gain bandwidths. We demonstrate this in devices using arrays of flux-focused SNAILs where flux biasing varies across the array. We find instantaneous bandwidths of 200 MHz with $>$17 dB of gain centred at $\sim$5.4 GHz in a device without a static impedance matcher. This broadening of amplifier bandwidth is stable with $>$100 MHz bandwidth at 17 dB gain across $>$1.2 GHz tunable bandwidth. Our analytical model captures flux dependence and qualitatively reproduces gain-bandwidths giving confidence in our understanding of these systems and allowing operational figures of merit to be optimised in future devices.

Comments
15 pages, 8 figures, main text and appendices

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Impedance matching is a crucial feature of an amplifier used to increase its instantaneous bandwidth and is typically achieved using static LC resonators. Here we show an approach to impedance matching in parametric amplifiers using arrays of unequal Josephson-junction-based elements (rf/dc SQUIDs, SNAILs, etc). The elements act either as small-footprint flux-tunable inductors forming an impedance-matching circuit, or 'active' amplifier elements which result in amplifier gain. We develop an analytical theory describing these systems, predicting a quasi-non-periodic amplifier frequency and gain modulation with applied flux and the broadening of gain bandwidths. We demonstrate this in devices using arrays of flux-focused SNAILs where flux biasing varies across the array. We find instantaneous bandwidths of 200 MHz with >>>17 dB of gain centred at ∼\sim∼5.4 GHz in a device without a static impedance matcher. This broadening of amplifier bandwidth is stable with >>>100 MHz bandwidth at 17 dB gain across >>>1.2 GHz tunable bandwidth. Our analytical model captures flux dependence and qualitatively reproduces gain-bandwidths giving confidence in our understanding of these systems and allowing operational figures of merit to be optimised in future devices.
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