image: Cited milestones in the evolution of superconducting qubit platforms: Transmon, Fluxonium, and Bosonic qubits.
Credit: ©Science China Press
A Review on Superconducting Quantum Computing
A recent review article published in National Science Review, led by the Beijing Academy of Quantum Information Sciences (BAQIS) and co-authored by over ten global research institutions, delivers a comprehensive overview of cutting-edge advancements in superconducting quantum computing (SQC). The study synthesizes interdisciplinary progress toward fault-tolerant quantum computation and scalable architectures, shedding light on technical breakthroughs that bridge theory and practical implementation.
Quantum Chip Fabrication: Materials and Integration
In the realm of hardware development, the authors highlight synergistic leaps in materials engineering, device architecture, and process integration. Aluminum remains the workhorse material due to its mature fabrication protocols, while tantalum is garnering attention for its potential to extend coherence times. Breakthroughs in Josephson junction fabrication—achieved via precise oxidation control and optimized thermal annealing—have substantially improved device uniformity and operational stability. Meanwhile, advanced interconnect technologies like flip-chip bonding and through-silicon vias (TSV) have leapfrogged integration density and mitigated crosstalk, pushing qubit energy relaxation times (T₁) into the millisecond regime. These innovations lay the physical foundation for next-generation superconducting processors.
Gate-Level Performance: Precision and Scalability
Multi-platform advancements in gate-level operations continue to accelerate. Single-qubit gates now commonly employ DRAG (Derivative Removal by Adiabatic Gate) pulse shaping to suppress leakage into non-computational states. Two-qubit gate implementations have evolved beyond traditional CR and CZ types, embracing parameter-modulated designs like fSim and bSWAP. When paired with tunable coupler architectures, these schemes enable faster gate operations and reduced crosstalk, with two-qubit error rates now dipping below 0.1% in select setups—approaching the threshold for fault-tolerant computation.
Multi-Qubit Control: Entanglement and Circuit Complexity
Experimental milestones in multi-qubit manipulation have reshaped scalability benchmarks. Zhejiang University recently generated GHZ-type entangled states across 60+ qubits with fidelities nearing 0.6, while the University of Science and Technology of China (USTC) pushed random quantum circuit sampling (RCS) to 83 qubits, achieving deeper circuit depths and enhanced measurement fidelity. Collectively, these feats demonstrate superconducting platforms’ growing capacity to sustain high-fidelity operations in complex quantum systems.
Fault Tolerance: From Theory to Experiment
A pivotal breakthrough came from Google, which experimentally verified that the logical error rate in a 105-qubit system could surpass the physical error rate—providing the first empirical evidence of surface code fault tolerance. Concurrently, quantum low-density parity-check (QLDPC) codes have emerged as viable alternatives, offering lower qubit overhead and robust error correction. For current noisy intermediate-scale quantum (NISQ) devices, error mitigation techniques like zero-noise extrapolation (ZNE) and probabilistic error cancellation (PEC) provide practical pathways to suppress errors without full-scale correction.
Novel Qubit Encodings: Beyond Conventional Architectures
Research into innovative qubit encoding schemes is gaining momentum. Bosonic codes—including cat codes, binomial codes, and Gottesman-Kitaev-Preskill (GKP) codes—harness the long coherence of superconducting cavities for logical information processing, with remote-controlled CNOT gates across cavity modes already demonstrated experimentally. Cat qubits exhibit inherent resilience against specific noise profiles, while fluxonium qubits—boasting tunable energy spectra and stable low-frequency operation—are emerging as promising candidates for scalable, next-generation architectures.
Challenges and Outlook
Despite these leaps, realizing universal quantum processors with millions of qubits remains a herculean task, demanding breakthroughs in scalable error correction, high-density interconnects, precise frequency calibration, and system-wide crosstalk suppression. Nevertheless, continuous improvements in coherence, gate fidelity, and integration are positioning SQC to deliver practical advantages in quantum chemistry, financial optimization, and combinatorial problem-solving—laying the groundwork for the eventual realization of fault-tolerant, large-scale quantum computing ecosystems.
See the article:
Advancements in Superconducting Quantum Computing
https://doi.org/10.1093/nsr/nwaf246
Journal
National Science Review