Materials exploration towards high coherence superconducting qubits

Superconducting quantum circuits are one of the leading platforms for quantum information processing. Tremendous progress has been made in extending the qubit lifetime over the past two decades. It has become clear that further improvement in qubit T1 is possible with reduction/elimination of lossy materials at various surfaces and interfaces by exploration of novel materials and fabrication processes. Our recent work at SQMS Center demonstrated T1 enhancement up to a factor of five in Nb qubits capped with a Ta passivation layer [1]. We attribute this improvement to the replacement of native Nb oxide layer with native Ta oxide, which is thinner and less disordered. We have expanded our work to explore annealing of Ta capped Nb films, substrate preparation, capping layers that do not form an oxide layer such as proximitized Au, and other superconducting base metal layers such as Ta and Re. The results of a systematic study, including the statistics of qubit T1 measurements, will be presented.

This material is based upon work supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract number DE-AC02-07CH11359.

[1] M. Bal et al., arXiv:2304.13257 (2023)