Reducing TLS loss in tantalum CPW resonators using titanium sacrificial layers
2026-01-30 10:53
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We demonstrate a substantial reduction in two-level system loss in tantalum coplanar waveguide resonators fabricated on high-resistivity silicon substrates
through the use of an ultrathin titanium sacrificial layer. A 0.2nm titanium film, deposited atop pre-sputtered {\alpha}-tantalum, acts as a solid-state oxygen getter
that chemically modifies the native Ta oxide at the metal-air interface. After device fabrication, the titanium layer is removed using buffered oxide etchant,
leaving behind a chemically reduced Ta oxide surface. Subsequent high-vacuum annealing further suppresses two-level system loss. Resonators treated with
this process exhibit internal quality factors Qi exceeding an average of 1.5 million in the single-photon regime across ten devices, over three times higher than
otherwise identical devices lacking the titanium layer. These 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.
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