What tiny superconductors need to become reliable quantum devices

A roadmap, not a single breakthrough

Superconductivity makes quantum behavior visible at the scale of electrical circuits. Electrons form pairs called Cooper pairs, and their collective state can maintain a shared quantum phase. This coherence underlies effects such as magnetic flux appearing in discrete units and current flowing without electrical resistance.

But these properties alone do not guarantee a useful device. Materials must be patterned, connected and measured without destroying the behavior researchers want to exploit.

The Roadmap on Nanoscale Superconductivity for Quantum Technologies surveys that problem through 23 contributions spanning materials, measurement tools and devices. It is published in Superconductor Science and Technology 39 (2026), 023502, with DOI 10.1088/1361-6668/ae3030. It emerged from SuperQuMap, a European research network involving groups in more than 30 countries, and includes perspectives from quantum-computing companies. Rather than reporting one new experiment, it reviews existing results, unresolved questions and possible routes forward.

Cleaner materials—and carefully placed defects

One recurring challenge is controlling interfaces: the boundaries where different materials meet. Stacking thin layers can combine superconductivity with magnetism or other electronic properties, creating behavior unavailable in either material alone. Yet contamination, structural disorder and imperfect contact can undermine those effects.

Twisting layered superconductors offers another control parameter. The roadmap describes cryogenic stacking methods that produce atomically sharp interfaces between copper-oxide superconductors. Building more elaborate circuits around these structures remains difficult because the materials are sensitive to heat, solvents and polymers.

Defects are not always undesirable, however. In many superconductors, magnetic field penetrates through vortices—structures carrying quantized magnetic flux. Moving vortices can cause dissipation. Deliberately introduced defects can hold them in place, improving current-carrying performance.

The useful distinction is therefore not simply between perfect and imperfect materials. It is between uncontrolled disorder and features engineered for a particular function. Focused helium-ion beams, for example, can locally suppress superconductivity in copper-oxide films, defining weak links or patterns that trap vortices without cutting away the film.

A promising signal is not proof

Some of the roadmap’s most ambitious proposals concern topological superconductors. These systems could host Majorana excitations, whose proposed uses include protecting quantum information.

The authors stress a crucial limitation: observing an electronic state at zero energy does not, by itself, establish topological superconductivity. Similar signals can arise from magnetic impurities, inhomogeneities and other mechanisms. More discriminating evidence is needed, potentially including measurements of the distinctive behavior of Majorana excitations when exchanged.

This makes better measurement tools central to the roadmap. Scanning tunnelling microscopes probe local electronic states, while scanning superconducting quantum interference devices, or SQUIDs, map magnetic flux. Angle-resolved photoemission spectroscopy measures how electronic states depend on energy and momentum.

Each technique reveals different information and has limits. A tunnelling microscope examines the surface, which need not behave like the bulk. Magnetic probes face trade-offs between spatial resolution and sensitivity. Combining complementary measurements is therefore important for identifying what a material actually does.

Different devices face different bottlenecks

The roadmap extends well beyond quantum processors. Superconducting nanowire detectors register individual photons when absorption triggers a temporary resistive region, producing an electrical pulse.

Research reviewed in the detector section demonstrates single-photon detection at temperatures up to 25 kelvin. That could ease cooling requirements, but these higher-temperature prototypes still have low efficiencies and incompletely understood detection mechanisms. Large detector arrays introduce separate challenges in uniform fabrication, readout and heat dissipation.

Josephson junctions—weak links between superconductors—connect many other applications. They are building blocks for magnetic sensors, microwave amplifiers and superconducting qubits. Their performance depends strongly on reproducible fabrication and low noise.

Scaling means more than adding qubits

For quantum computing, the roadmap describes progress in coherence, gate operations and error correction, while emphasizing the remaining systems problem. Reliable logical qubits require error-correction protocols that distribute information across many physical qubits.

Increasing their number also increases demands on wiring, packaging, control electronics and refrigeration. The authors discuss three-dimensional interconnects, multichip modules and shared control schemes as possible ways forward—not completed solutions.

Higher superconducting transition temperatures do not automatically remove these requirements: the processor section describes operation around 20 millikelvin to suppress thermal excitation.

The roadmap’s practical message is that no single material or fabrication advance resolves every bottleneck. Progress must connect convincing evidence of quantum behavior with reproducible components and engineering that preserves their performance at larger scales.