Quantum information science has entered its second phase, enabling more complex computations and sensing technologies than previously possible. This new era demands advances in materials science as limitations now stem less from device design and increasingly from poorly defined material properties across multiple platforms including superconducting circuits and two-dimensional materials. More powerful quantum computers are now constrained not by design but by imperfections within constituent materials; this ‘structure-coherence problem’ affects various types of hardware including superconducting circuits and two-dimensional materials.

These limitations arise from poorly understood atomic-scale surfaces, interfaces and defects which degrade performance across all solid-state platforms. Addressing these fundamental material issues is essential for creating larger, more reliable quantum processors capable of exceeding current capabilities. Material imperfections increasingly limit advances in quantum computing hardware, whereas previously, design limitations were the primary obstacle.

This shift marks ‘Quantum Evolution 2.0’, where building scalable multi-qubit processors demands deeper understanding of atomic-scale defects within solid-state platforms like superconducting circuits and two-dimensional materials, extremely thin layers stacked together much like LEGO bricks. A key challenge is decoherence, a gradual loss of signal clarity akin to increasing static interference on a radio, impacting performance across all systems.

While progress has been made with single qubits and achieving high accuracy in operations, scaling up these devices requires addressing fundamental material issues that affect reproducibility and integration. The team will now detail specific challenges for each platform alongside shared problems hindering the field; new characterisation tools may unlock solutions to improve coherence and scalability before current limitations are reached.

Revealing Atomic Defects Limiting Quantum Device Performance

Atom probe tomography proved central to revealing these material limitations across diverse quantum hardware. The technique fires a pulsed laser at a sample tip; each pulse sputters away individual atoms projected onto a detector via electric fields. By recording the time-of-flight and position of arrival for millions of ions, it reconstructs a three-dimensional map of atomic composition with near-atomic resolution, effectively creating an elemental ‘fingerprint’ of the material’s structure.

This method isn’t limited to surface observations but penetrates beneath layers allowing detailed examination of buried interfaces where defects often originate. Current restrictions stem not from device designs but from poorly controlled surfaces and defects within materials used in superconducting circuits, photonic devices and two-dimensional heterostructures.

Material surface imperfections limit advances in multi-qubit gate fidelity

Multi-qubit gate fidelities have exceeding 9x%, a threshold previously unattainable due to limitations in coherent control established during initial quantum computing development. The review demonstrates that current restrictions on advancing quantum information science now arise from poorly defined material properties; specifically uncontrolled surfaces and defects with unknown atomic identities are more impactful than solely device engineering challenges. This ‘structure-coherence problem’ impacts diverse hardware platforms including superconducting circuits, photonic devices, and emerging two-dimensional materials where light elements within disordered environments contribute sharply to decoherence.

Investigations detailed how tantalum deposited directly onto sapphire exhibited increased signal loss, while niobium showed no such detrimental effect when grown under identical conditions. Substrate materials were also investigated revealing acceptor dopants like boron within silicon substrates create a ‘two-level system’ bath which actively diminishes coherence, highlighting the need for ultrapure base materials.

Optimisation of deposition techniques proved important too; high power direct current magnetron sputtering yielded larger niobium grains and improved device performance compared to alternative methods, with even altering process gases from argon to krypton during deposition lowering temperatures needed to achieve desired material phases. These findings demonstrate fabrication steps strongly influence defect landscapes beyond intrinsic material properties, often creating new decoherence pathways whilst attempting to resolve existing ones.

Atomic disorder as a primary limitation on quantum coherence durations

The pursuit of scalable quantum computers has demonstrably shifted focus from perfecting qubit control towards understanding, and mitigating, the impact of material imperfections. Previously attention centred on improving device fabrication techniques and achieving longer coherence times; however, this review stresses a more fundamental challenge: poorly defined atomic structures are now limiting progress across diverse hardware platforms like superconducting circuits and two-dimensional materials. Identifying common material chemistry, particularly light elements within disordered layers, provides key targets for improvement efforts, even without precise quantification reducing these known problematic areas will likely yield performance gains.

This analysis reveals a critical juncture for quantum information science where limitations are dictated by material properties rather than solely device fabrication techniques. Deeper investigation into surfaces, interfaces and defects is therefore necessary in materials used across diverse platforms such as superconducting circuits and two-dimensional heterostructures, which comprise multiple layers stacked together. Identifying recurring problematic chemistry involving light elements embedded within disordered environments suggests opportunities to develop broadly applicable solutions improving coherence, maintaining signal clarity, and scalability.

The research demonstrated that poorly defined atomic structures now limit the development of scalable quantum computers across various hardware platforms. This means improvements to devices are currently hindered more by imperfections in the materials themselves than by how those devices are built. Researchers identified common material issues, specifically relating to lighter elements found in disordered or buried layers, suggesting a shared problem impacting different qubit technologies. The authors highlight a need for better characterisation tools and understanding of these defects to improve device performance and maintain signal integrity.

👉 More information
🗞 Materials for Quantum Information Science: Roles in the Quantum Evolution 2.0
✍️ Thang Pham, Vsevolod Ivanov, Dominic P. Goronzy, Abhiram Devata, Joshua Feldon, David Barton and You Zhou
🧠 ArXiv: https://arxiv.org/abs/2609.09371

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