Spotting a New Culprit in the Hunt for Quantum Noise
Microscopes, x-rays, and spectroscopy tools join forces to identify defects that interfere with delicate superconducting qubit properties.
The Science
Quantum computers rely on qubits, the quantum version of bits in classical computers. Some of these qubits use superconducting materials that carry electrical current with no resistance. Stable superconductivity allows researchers access to the quantum properties of matter. However, imperfections in superconducting devices can create “noise” or interference. In quantum systems, this is called decoherence and limits how long qubits can store information. Scientists are working to identify what drives decoherence and how to eliminate it. In this study, researchers examined how imperfections form in the material niobium. Researchers combined several experimental techniques, including atomic-force microscopy, X-ray diffraction, and mass spectrometry. With these tools, they identified the formation of one type of defect called niobium hydrides.
The Impact
Now that scientists have identified this type of defect, they can work to prevent niobium hydrides from forming in materials. They can address this problem by adjusting how they engineer materials and devices. They can also improve their control over which gases the devices encounter during fabrication. With less noise, quantum computers could operate with fewer errors. This could let researchers run larger calculations more accurately. Quantum computers have applications across many fields, including chemistry, physics, and cybersecurity. This insight will also help scientists build more sensitive quantum sensors from superconducting materials. Because sensors like this can measure electric, magnetic, and gravitational fields, researchers can use them in several types of research.
Summary
To search for niobium hydrides, the team used qubits fabricated by industry partners at Rigetti Computing. The team cooled the qubits from room temperature to 2 K (Kelvins) and performed atomic force microscopy at 50 K intervals. During the cooldown, the researchers observed new features forming near the surface of the qubits. Next, the researchers used time-of-flight secondary ion mass spectrometry to probe the hydrogen concentration in the material. Lastly, they used x-ray diffraction to characterize the crystal phases. For each measurement, the researchers compared their results with previous work on bulk niobium in cavities and confirmed the presence of similar niobium hydride signals.
The research findings suggest that niobium hydrides commonly form in niobium thin films. This information introduces a previously unaccounted-for source of decoherence in superconducting qubits and other resonators. The size, location, and density of these niobium hydrides can vary as researchers cool devices from room temperature. Learning how these hydrides form may help explain why qubits do not perform identically each time. Now that researchers understand these effects more clearly, they may be able to limit hydride formation by using techniques such as strategically introducing other impurities to sequester hydrogen and reduce this source of noise.
Contact
Zu Hawn Sung
Fermilab
zsung@fnal.gov
Funding
All research funding for this publication came through the DOE’s support of the Superconducting Quantum Materials and Systems Center, a National QIS Research Center led by Fermilab. The facilities where the experiments were conducted are also supported by the Spanish Ministerio de Ciencia, Innovación y Universidades and Consejo Superior de Investigaciones Científicas, the National Science Foundation, the International Institute for Nanotechnology, the Keck Foundation, and the State of Illinois.
Publications
Z-H Sung, et al. “Discovery of niobium hydride precipitates in superconducting qubits”, Phys. Rev. Materials 10, 016201 (2026). [DOI: 10.1103/mgnw-kjps]
Related Links
Discovery of niobium hydride precipitates in superconducting qubits, Fermilab News
Highlight Categories
Performer: DOE Laboratory
Additional: International Collaboration
