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arXiv:2603.09096

Reconfigurable Superconducting Quantum Circuits Enabled by Micro-Scale Liquid-Metal Interconnects

Zhancheng Yao, Nicholas E. Fuhr, Nicholas Russo, David W. Abraham, Kevin E. Smith, David J. Bishop

quant-phcond-mat.mtrl-sciSubmitted Mar 10, 2026• Announced Mar 11, 2026• 0 citations
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Abstract

Modular architectures are a promising route toward scalable superconducting quantum processors, but finite fabrication yield and the lack of high quality temporary interconnects impose fundamental limitations on system size. Here, we demonstrate chip-scale liquid-metal interconnects that show promise for plug-and-play superconducting quantum circuits by enabling non-destructive module replacement while maintaining high microwave performance. Using gallium-based liquid metals, we realize high-quality inter-module signal and ground interconnects, comparable in performance to conventional coplanar waveguide resonators. We illustrate consistent device characteristics across three thermal cycles between room temperature and 15 mK, as well as the ability to reform superconducting connections following module replacement. A width-dependent resonance frequency shift reveals a significant kinetic inductance fraction, which we attribute to the presence of $β$-phase tantalum as confirmed by X-ray characterization. Finally, we investigate power-dependent loss mechanisms and observe high-power dissipative nonlinearities qualitatively consistent with a readout-power heating model. These results establish liquid metals as viable chip-scale interconnects for reconfigurable, modular superconducting quantum systems.

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Modular architectures are a promising route toward scalable superconducting quantum processors, but finite fabrication yield and the lack of high quality temporary interconnects impose fundamental limitations on system size. Here, we demonstrate chip-scale liquid-metal interconnects that show promise for plug-and-play superconducting quantum circuits by enabling non-destructive module replacement while maintaining high microwave performance. Using gallium-based liquid metals, we realize high-quality inter-module signal and ground interconnects, comparable in performance to conventional coplanar waveguide resonators. We illustrate consistent device characteristics across three thermal cycles between room temperature and 15 mK, as well as the ability to reform superconducting connections following module replacement. A width-dependent resonance frequency shift reveals a significant kinetic inductance fraction, which we attribute to the presence of βββ-phase tantalum as confirmed by X-ray characterization. Finally, we investigate power-dependent loss mechanisms and observe high-power dissipative nonlinearities qualitatively consistent with a readout-power heating model. These results establish liquid metals as viable chip-scale interconnects for reconfigurable, modular superconducting quantum systems.
Building a modular architecture with superconducting quantum computing chips is one of the means to achieve qubit scalability, allowing the screening, selection, replacement, and integration of individual qubit modules into large quantum systems. However, the nondestructive replacement of modules within a compact architecture remains a challenge. Liquid metals, specifically gallium alloys, can be alternatives to solid-state galvanic interconnects. This is motivated by their self-healing, self-aligning, and other desirable fluidic properties, potentially enabling the nondestructive replacement of modules at room temperatures, even after operating the entire system at millikelvin regimes. In this study, we present coplanar waveguide resonators (CPWRs) interconnected by gallium alloy droplets, achieving high internal quality factors up to nearly one million and demonstrating performance on par with the continuous solid-state CPWRs. Leveraging the desirable fluidic properties of gallium alloys at room temperature and their compact design, we envision a modular quantum system enabled by liquid metals.
Abstract Reproducible low-loss microwave interconnects are essential for scaling modular superconducting quantum processors and networks. Wire bonds provide a simple and flexible route to galvanic connections in such systems, but their microwave loss and reproducibility at millikelvin temperatures remain insufficiently quantified. Here we demonstrate reproducible low-loss aluminum wire-bond interconnects in both superconducting cable resonators and planar tantalum resonators. In the cable devices, a wire-bond connection is placed at the midpoint of a high-quality resonator, where the different current distributions of odd and even modes separate connection-induced loss from intrinsic cable dissipation within the same device. Across devices fabricated with different bond numbers and ultrasonic powers, a stable bonding window yields no resolvable connection resistance above the practical resolution of order 0.1 m Ω . Measurements of planar resonators on two chips independently show no systematic degradation of the internal quality factor from wire-bond ground terminations within the device-to-device variation. These results establish aluminum wire bonding as a reproducible low-loss interconnect for superconducting microwave circuits, supporting the scalable assembly of modular superconducting quantum processors and networks.
The performance and scalability of superconducting quantum circuits are fundamentally constrained by non-equilibrium quasiparticles, which induce microwave losses that limit resonator quality factors and qubit coherence times. Understanding and mitigating these excitations is therefore central to advancing scalable quantum technologies. Here, we demonstrate on-chip microwave sensing of quasiparticles in high-Q α-tantalum coplanar waveguide resonators on silicon, operated in the single-photon regime. Temperature-dependent measurements reveal persistent non-equilibrium quasiparticles at millikelvin temperatures, producing a measurable suppression of the internal quality factor (Qi) relative to theoretical expectations. By benchmarking across materials, we find that the quasiparticle density in α-Ta is approximately one-third that of NbN at equivalent normalised temperatures (T/Tc), directly correlating with reduced microwave loss. Our methodology establishes a scalable platform for probing quasiparticle dynamics and points towards new routes for engineering superconducting circuits with improved coherence, with impact on qubit readout resonators, kinetic-inductance detectors, and emerging quantum processors and sensors.
Superconducting circuits are a promising platform for implementing fault-tolerant quantum computers, quantum limited amplifiers, ultra-low power superconducting electronics, and sensors with ultimate sensitivity. Typically, circuit fabrication is realized by standard nanolithography, generally associated with a high level of control over defects and contaminants. Additive approaches have not been used so far since they are expected to be inferior in terms of superconducting properties or quantum coherence. This work shows that liquid-metal based micro-pipette printing is suited for fabricating superconducting lumped-element resonators with high internal quality factors. The applicability of our technique for low-loss superconducting device fabrication and the possibility to locally add metal structures, without affecting any preexisting circuit elements, is a further advantage. Our results open up new avenues in the hardware implementation of scaled-up superconducting quantum computers.
High Resolution Image Download MS PowerPoint Slide The performance and scalability of superconducting quantum circuits are fundamentally constrained by nonequilibrium quasiparticles, which induce microwave losses that limit resonator quality factors and qubit coherence times. Understanding and mitigating these excitations is therefore central to advancing scalable quantum technologies. Here, we demonstrate on-chip microwave sensing of quasiparticles in high- Q α -tantalum coplanar waveguide resonators on silicon, operated in the single-photon regime. Temperature-dependent measurements reveal persistent nonequilibrium quasiparticles at millikelvin temperatures, producing a measurable suppression of the internal quality factor ( Q i ) relative to theoretical expectations. By benchmarking across materials, we find that the quasiparticle density in α-Ta is approximately one-third that of NbN at equivalent normalized temperatures ( T / T c ), directly correlating with reduced microwave loss. Our methodology establishes a scalable platform for probing quasiparticle dynamics and points toward new routes for engineering superconducting circuits with improved coherence, with impact on qubit readout resonators, kinetic-inductance detectors, and emerging quantum processors and sensors.
We have demonstrated superconducting interconnect technologies that enable a variety of flip-chip 3D integrated structures and packages compatible with high-coherence superconducting qubits. Superconducting indium micro-bumps and underbump metal (UBM) were used to join superconducting qubit chips to superconducting readout and control modules while maintaining high qubit coherence (T1, T2,echo> 20 μs) in the presence of capacitive and inductive coupling between the chips. Scanning electron microscope, X-ray, infrared and confocal microscopy were used to investigate the micro-structure, alignment accuracy, and parallelism of flip-chip qubits. The superconducting readout and control modules can accommodate both niobium and aluminum-based circuit and amplifier fabrication processes, including shadow-evaporated aluminum or Nb/Al-AlOx/Nb trilayer Josephson junctions (JJs). We present results for up to 16 active superconducting chips having trilayer junctions bonded to a passive superconducting module. The I-V characteristics and switching behavior were measured for flip-chip-connected JJ arrays with 40-20,000 JJs. Our approach maintained chip-level junction critical current and qubit coherence, demonstrating it to be a viable approach to building larger quantum computing systems. This paper also discusses packaging approaches to developing a quantum-to-classical interface in a cryogenic environment with multiple temperature stages.