Researchers from the University of California, Berkeley, led by Zachary Degnan and including Chun-Ching Chiu, Yi-Hsun Chen, David Sommers, Leonid Abdurakhimov, Lihuang Zhu, Arkady Fedorov, and Peter Jacobson, have made a significant advancement in reducing energy loss in tantalum-based superconducting circuits. Their work, published in the journal Applied Physics Letters, focuses on improving the performance of quantum circuits used in advanced computing and energy technologies.
The team demonstrated a substantial reduction in two-level system loss in tantalum coplanar waveguide resonators. These resonators are fabricated on high-resistivity silicon substrates and are crucial components in superconducting quantum circuits. The researchers introduced an ultrathin titanium sacrificial layer, just 0.2 nanometers thick, deposited atop pre-sputtered α-tantalum. This titanium layer acts as a solid-state oxygen getter, chemically modifying the native tantalum oxide at the metal-air interface.
After device fabrication, the titanium layer is removed using buffered oxide etchant, leaving behind a chemically reduced tantalum oxide surface. Subsequent high-vacuum annealing further suppresses two-level system loss. Resonators treated with this process exhibit internal quality factors exceeding an average of 1.5 million in the single-photon regime across ten devices. This is over three times higher than otherwise identical devices lacking the titanium layer.
The results highlight the critical role of interfacial oxide chemistry in superconducting loss and reinforce atomic-scale surface engineering as an effective approach to improving coherence in tantalum-based quantum circuits. The method is compatible with existing fabrication workflows applicable to tantalum films, offering a practical route to further extending T1 lifetimes in superconducting qubits. This advancement could have significant implications for the energy sector, particularly in the development of more efficient and reliable quantum computing technologies, which can be applied to optimize energy systems and improve energy storage solutions.
The research was published in the journal Applied Physics Letters, providing a clear path forward for enhancing the performance of tantalum-based superconducting circuits.
This article is based on research available at arXiv.