Advancing Quantum Technology: Tantalum's Impact on Next Generation Qubits
Enhancing quantum coherence through innovative materials design in superconducting circuits
The Science
Superconducting quantum circuits are one way to make quantum bits, or qubits, the building blocks at the heart of quantum computers. Qubits store information using a phenomenon called coherence. Maintaining coherence takes energy and, like all electronics, qubits can lose energy. However, researchers haven’t solved the challenge of exactly how qubits lose their energy and how to reduce that loss. Determining the key sources of energy loss and adjusting how qubits are made can help researchers design new devices that retain coherence and thus quantum information for longer amounts of time. In this study, researchers presented a novel way to characterize energy losses using devices called thin-film resonators. The work found that the shape of the resonator influences energy loss. The study compared devices made of tantalum versus devices made of aluminum. It also compared devices with a sapphire base, or substrate, that was treated using a process called annealing versus an untreated substrate. The results found that the devices made of tantalum with annealed sapphire substrates had substantially better performance.
The Impact
The research showed that quantum devices made using materials based on tantalum and with optimized circuit layout reduced qubit energy loss and improved coherence times. The research used a novel tripole stripline device with three superconducting strips. This device allowed the researchers to test different variables and to tease out different ways superconducting circuits can lose energy, a notoriously difficult problem. The findings offer a versatile method that can be adapted to various quantum circuit designs. The result is a significant step towards scalable and reliable quantum computing components. It paves the way for compact and modular superconducting qubits. These advances could accelerate progress toward better qubits that offer low energy and information loss.
Summary
In this study, researchers introduced a comprehensive technique for characterizing microwave losses in superconducting thin-film resonators. They showed that resonator geometry significantly affects surface, bulk, and package losses. In addition, they showed that tantalum-based qubits yield higher internal quality factors due to improved surface quality and that annealing sapphire substrates results in dramatically reduced bulk dielectric losses. The team also showed that by understanding the sources of loss in superconducting resonators, they could predict and experimentally verify losses in co-fabricated transmon qubits. This allowed them to optimize qubit design to improve their coherence. These insights led to the development of an optimized stripline-based quantum memory using thin-film superconductors patterned on a substrate. This architecture enables a coaxial design that is more scalable, modular, and compact than traditional cavity approaches.
The stripline-based quantum memory exhibited millisecond Ramsey coherence times, making it suitable for scalable multiqubit systems. The architecture allows for noise-biased qubits, potentially lowering error correction thresholds for implementing surface codes of dual-rail qubits. Moreover, loss characterization revealed that reducing surface participation near the Josephson junction and reducing bulk dielectric losses are critical for enhancing coherence in transmon qubits. Overall, this work provides valuable insights into coherence-limiting mechanisms and new techniques for characterizing losses. These results can inform new design principles for superconducting quantum circuits and offering a promising path toward robust quantum computing with bosonic modes.
Contact
Suhas Ganjam[email protected]
Funding
This research was supported in part by the Department of Energy (DOE) Office of Science, National Quantum Information Science Research Centers, Co-design Center for Quantum Advantage (C2QA) and by the U.S. Army Research Office. This research used the Electron Microscopy and Materials Synthesis & Characterization facilities at the Center for Functional Nanomaterials, a DOE Office of Science user facility at Brookhaven National Laboratory. The use of fabrication facilities was supported by the Yale Institute for Nanoscience and Quantum Engineering and the Yale SEAS Cleanroom.
Publications
Ganjam, S., et al., Surpassing millisecond coherence in on chip superconducting quantum memories by optimizing materials and circuit design. Nature Communications 15, 3687 (2024). [DOI: 10.1038/s41467-024-47857-6]
Related Links
Studying Loss to Make Quantum Computing Gains, Brookhaven National Laboratory Newsroom
