Advances in Josephson Junction Materials and Processes Toward Practical Quantum Computing
Hyunseong Linus Kim, Gyunghyun Jang, Seungwon Jin, Jaewon An, Hyeon‐Jin Shin, Hyeon‐Jin Shin, Jie Luo, Akel Hashim, Irfan A. Siddiqi, Yosep Kim, Long B. Nguyen, Hoon Hahn Yoon
The Josephson junction (JJ) is the fundamental nonlinear building block of superconducting quantum technologies. Its macroscopic quantum tunneling physics underpins superconducting quantum computing, sensing, and communication, but scaling these platforms to utility-scale architectures places increasingly stringent demands on junction materials, interfaces, and fabrication. Practical quantum computing requires high reproducibility, low power consumption, tunability, a small device footprint, and resilience to noise and defects. This review surveys how advances in materials science, device characterization, and nanofabrication are addressing these challenges and redefining the figures of merit for next-generation JJs. This review also examines the evolution of fabrication strategies, from conventional multi-angle evaporation to foundry-compatible superconducting processes and the integration of emerging junction materials. Progress along these directions will determine how rapidly JJs move from laboratory-scale components to the foundation of industrial-scale quantum processors.
The Josephson junction (JJ) is the fundamental nonlinear building block of superconducting quantum technologies. Its macroscopic quantum tunneling physics underpins superconducting quantum computing, sensing, and communication, but scaling these platforms to utility-scale architectures places increasingly stringent demands on junction materials, interfaces, and fabrication. Practical quantum computing requires high reproducibility, low power consumption, tunability, a small device footprint, and resilience to noise and defects. This review surveys how advances in materials science, device characterization, and nanofabrication are addressing these challenges and redefining the figures of merit for next-generation JJs. This review also examines the evolution of fabrication strategies, from conventional multi-angle evaporation to foundry-compatible superconducting processes and the integration of emerging junction materials. Progress along these directions will determine how rapidly JJs move from laboratory-scale components to the foundation of industrial-scale quantum processors.
Quantum processing units (QPUs) built on superconducting Josephson junctions remain the most industrially mature route to fault-tolerant quantum computing, but the field has moved substantially since early 2025. This paper provides an updated overview of Josephson-junction QPUs, grounded in the quantum-mechanical principles, superposition, entanglement, and decoherence, that any qubit implementation must contend with, and in the physics of Cooper pairing and quantum tunneling that make a Josephson junction behave as a controllable qubit. We examine the engineering challenges of scaling these devices, including crosstalk, classical control-interface bottlenecks, and quantum error correction, and discuss the first below-threshold surface-code demonstrations on superconducting hardware. We survey recent materials advances, near-term computational results, and applications beyond computing, and compare Josephson-junction QPUs against trapped-ion, photonic, and neutral-atom alternatives, the latter having emerged as a serious fourth architecture since our original analysis. We close with the current public roadmaps toward fault-tolerant superconducting quantum computers and a calibrated assessment of how much progress those roadmaps still require.
Superconducting (SC) electronics have emerged as a promising platform for high-speed, energy-efficient computing and quantum information processing. This work, centered on NbTiN, presents recent advances in material science and fabrication methods leading to significant improvements in performance, scalability and vertical integration. We specifically report on fabrication and characterization of key components, including Josephson junctions (JJs), flux trapping structures and SC interconnects. Together, these efforts represent critical steps towards realizing practical, complex, dense and large-scale SC integrated circuits.
Quantum computing is rapidly evolving from theoretical frameworks to functional hardware, with physical qubits now being realized across multiple experimental platforms. Precision nanofabrication has enabled the development of low-loss, high-coherence quantum devices. Among the various approaches, superconducting circuits and trapped-ion systems have emerged as the most advanced and experimentally successful platforms for realizing controllable and scalable qubits. This review presents an overview of nanoscale fabrication techniques employed in these two architectures. We first outline the operating principles that define qubit behavior, followed by a discussion of representative device designs and fabrication workflows. In superconducting circuits, we examine processes such as thin-film deposition, lithographic patterning, and Josephson-junction fabrication that determine key parameters including qubit frequency, anharmonicity, and coherence. For trapped-ion systems, we describe the transition from bulk electrode assemblies to microfabricated surface traps produced using photolithography, metal deposition, and dielectric layering, where electrode geometry and surface treatment directly influence ion confinement and motional heating. We further discuss fabrication-related challenges, including dielectric loss, surface contamination, and material defects that limit coherence and reproducibility, along with emerging mitigation strategies such as advanced cleaning, low-loss materials, and improved surface engineering. By drawing parallels between these two leading platforms, this review highlights that continued progress in nanofabrication remains central to realizing scalable, high-fidelity quantum processors.
Abstract: The rapid advancement of quantum computing is largely driven by innovations in quantum chip architectures, with superconducting and topological qubits emerging as the most promising candidates for scalable and fault-tolerant quantum processors. Superconducting qubits, built using Josephson junctions, have demonstrated significant progress in coherence time, gate fidelity, and quantum error correction, making them the backbone of leading quantum processors such as IBM’s Eagle and Google’s Sycamore. Meanwhile, topological qubits, based on Majorana zero modes (MZMs) and non-Abelian anyons, offer intrinsic error resistance, reducing the computational overhead required for fault-tolerant quantum operations. This chapter explores the fundamental principles, fabrication techniques, and scalability challenges associated with these next-generation quantum chips, highlighting key advancements in hybrid quantum architectures, quantum error mitigation, and cryogenic quantum-classical interfacing. Additionally, it examines the geopolitical and ethical considerations of quantum supremacy, along with the transformative impact of next-gen quantum chips on AI, cryptography, materials science, and optimization problems. As research accelerates, the path toward scalable, fault-tolerant quantum computing is becoming clearer, paving the way for a future where quantum processors outperform classical supercomputers in solving the world’s most complex challenges. Keywords: Quantum chips, superconducting qubits, topological qubits, Josephson junctions, Majorana zero modes, quantum error correction, hybrid quantum architectures, fault-tolerant quantum computing, cryogenic electronics, quantum-classical interfacing, scalable quantum processors, AI-driven quantum computing, quantum supremacy, post-quantum cryptography, nanofabrication, quantum hardware innovation
Superconducting and photonic qubits are the two promising platforms for quantum computation. This review investigates different materials that are being used to advance these platforms, detailing the structural, electrical, and thermal properties that influence qubit performance. The discussion on superconducting qubits covers material properties critical for achieving low-loss circuits, the impact of two-level system defects, and the engineering of Josephson junctions. In contrast, photonic qubits, which leverage light for quantum information processing, are examined through the lens of material platforms such as silicon-based photonics and III–V semiconductors. The chapter also highlights fabrication challenges, qubit coherence improvements, and recent advances in single-photon sources for scalable quantum systems. By analyzing the intersection of materials science, quantum mechanics, and device engineering, this review provides insights into the optimization of quantum hardware for future large-scale quantum computing applications.
Superconducting circuits have emerged as a highly promising platform for quantum computing, among other divices based on Josephson junctions. The fabrication and testing of these devices requires especiallized nanofabrication facilities and milikelvin range testing equipment. In the search for the fabrication of these devices we have ran into limitations which forced us into creative solutions for the fabrications of these superconducting circuits and Josephson Junctions. Furthermore the development of these technologies allows for application in a wide range of research fields such as quantum computing, magnonics, micro-electromechanical systems and more.