Simple Chemical Tackle Unlocks Quantum Computing's Holy Grail: Surface Encapsulation Breakthrough Extends Qubit Coherence Times Fivefold

Researchers at the SQMS Center have achieved a breakthrough in quantum computing by developing a surface encapsulation technique that prevents lossy oxide formation on niobium qubits, extending coherence times by 2-5x and bringing practical quantum applications significantly closer to reality.

Researchers at the U.S. Department of Energy's Fermi National Accelerator Laboratory have achieved a significant breakthrough in quantum computing that could accelerate the path toward practical, energy-efficient quantum applications. Through the Superconducting Quantum Materials and Systems (SQMS) Center, a team of scientists has developed a surface encapsulation technique that dramatically improves the performance of superconducting qubits by preventing the formation of lossy surface oxides.

The breakthrough, published in npj Quantum Information in 2024, demonstrates that by encapsulating niobium qubit surfaces with materials such as tantalum, gold, titanium nitride, and aluminum, researchers can systematically increase T1 relaxation times—the measure of how long a qubit maintains its quantum state—by two to five times compared to baseline devices with native niobium oxides.

"We present a transmon qubit fabrication technique that yields systematic improvements in T1 relaxation times," the research team wrote in their paper. "We encapsulate the surface of niobium and prevent the formation of its lossy surface oxide."

The results are striking. When capping niobium with tantalum, the researchers obtained average qubit lifetimes above 200 microseconds, with median lifetimes exceeding 300 microseconds. Tantalum and gold proved to be the most effective capping layers, enabling average coherence times of 0.3 milliseconds and maximum values as high as 0.6 milliseconds—among the highest lifetimes reported to date for superconducting qubits prepared on both sapphire and silicon substrates.

The significance of this breakthrough extends far beyond the laboratory. Coherence time is one of the most critical limitations in quantum computing, determining how long quantum algorithms can run before environmental noise destroys the delicate quantum information. Current superconducting qubits typically maintain coherence for only 50 to 300 microseconds, creating severe constraints on computational complexity.

By extending coherence times through a relatively simple chemical modification—encapsulating the qubit surface before exposure to air—this technique addresses one of quantum computing's fundamental engineering challenges. The approach is also highly practical: it is scalable, compatible with industrial cleanroom processes, and can be directly implemented to improve the performance of mid-scale quantum processor prototypes.

The research represents a collaboration between Fermilab's SQMS Center, Northwestern University, Rigetti Computing, Ames National Laboratory, NIST Boulder, and Louisiana State University. SQMS researchers from Fermilab and Rigetti have already co-developed a 9-qubit transmon qubit chip-based processor incorporating these advances.

Why it matters

This breakthrough brings quantum computing significantly closer to practical applications by solving one of the field's most persistent engineering challenges. Longer coherence times mean quantum computers can run more complex algorithms, perform more calculations before errors accumulate, and move closer to achieving "quantum advantage"—solving problems that classical computers cannot. The technique's scalability and industrial compatibility suggest that practical quantum computing applications in drug discovery, materials science, optimization, and cryptography may arrive sooner than previously anticipated.

Background

Superconducting qubits are among the most promising platforms for building practical quantum computers, with companies like IBM, Google, and Rigetti making significant advances in recent years. However, these qubits are extremely sensitive to environmental noise and material defects. One major source of decoherence has been the formation of native oxides on the surface of niobium, the superconducting metal commonly used in transmon qubits. These oxides create "two-level systems"—defects that absorb and dissipate energy, shortening the qubit's coherence time. The SQMS Center's surface encapsulation strategy directly addresses this problem by preventing oxide formation through a protective capping layer.

What's next

The SQMS Center and its collaborators are continuing to refine the surface encapsulation technique and integrate it into larger-scale quantum processors. The approach is already being incorporated into 9-qubit chips and could scale to much larger systems. Researchers are also exploring alternative encapsulation materials and surface treatments that could push coherence times even higher. As these material improvements combine with advances in quantum error correction and algorithm design, the path toward practical quantum computing applications continues to accelerate.