MIT shields ultrathin superconductor for smaller quantum circuits

MIT Researchers Develop Air-Stable Ultrathin Superconductor for Quantum Circuits

Two-dimensional superconductors hold strong potential for shrinking superconducting circuitry because they maintain their superconducting properties while being only a few atoms thick. Niobium diselenide, composed of a single layer of niobium atoms sandwiched between selenium layers, features exceptionally high kinetic inductance. This property allows the material to store substantial inductive energy in a compact footprint.

Conventionally, quantum circuits achieve similar effects using arrays of electronic devices called Josephson junctions, which demand considerably more space. Incorporating thin films of niobium diselenide could replace those larger junction arrays, enabling more compact quantum computing hardware and ultrasensitive quantum detectors utilized in communications and cosmology, according to reports from MIT News.

Encapsulation Epitaxy Overcomes Air Degradation

Historically, working with niobium diselenide at scale has proved difficult. Once created and removed from controlled environments, the material typically oxidizes and degrades almost immediately, forcing scientists to rely on tiny flakes produced via exfoliation.

To solve this obstacle, the MIT team devised a method termed encapsulation epitaxy. Instead of growing the superconductor first and applying a protective coating afterward, researchers place a sheet of graphene on top of a silicon dioxide substrate before introducing chemical precursors.

Within the narrow gap of less than one nanometre between the graphene and the substrate, the niobium diselenide crystallizes. The silicon dioxide traps the precursors long enough for crystal formation to begin, while the graphene layer allows the material to spread smoothly into a continuous monolayer while shielding it from ambient oxygen.

Using this technique, the team successfully produced uniform niobium diselenide films measuring more than an inch across. According to Graphene-Info, these heterostructures exhibited a superconducting transition temperature of approximately 1 K and an enhanced charge density wave transition temperature of roughly 177 K.

Integration Into Microwave Circuits

Following growth, the team developed an oxidation-free transfer process and a superconducting edge-contact method to integrate the material into a working superconducting microwave circuit. Testing revealed that the niobium diselenide retained its superconducting behavior after fabrication and exhibited a measured kinetic inductance of approximately 0.7 nH per square.

Emerging superconductors that are only a monolayer thick have a lot of potential, said Xudong Sheldon Zheng, an EECS graduate student at MIT and co-lead author of the study, as reported by Tech Explorist. Thanks to our new process, they are no longer materials that can only be made at a very small scale.

Co-lead author Sameia Zaman, also an EECS graduate student at MIT, noted that the process creates new opportunities for scientific exploration. We've taken a very good step toward exploring both the physics and the application side of this thin, monolayer superconductor, Zaman said.

Collaborative Scope and Future Steps

The research involved MIT alongside partners from Harvard University, Rice University, Yale University, MIT Lincoln Laboratory, and Pohang University in South Korea.

Investigators emphasize that the encapsulation epitaxy technique is not restricted to niobium diselenide alone. The growth strategy can be extended to other atomically thin quantum materials with distinct properties.

While the recent experiments do not yet demonstrate a complete, functional miniaturized quantum device, the development provides a viable route toward compact circuits and scalable quantum technologies. Moving forward, the research team plans to integrate the material into functional quantum-device architectures while continuing to investigate its underlying physics and practical applications.