Abstract
Continued advances in superconducting qubit performance require more detailed understandings of the many sources of decoherence. Within these devices, two-level systems arise due to defects, interfaces, and grain boundaries and are thought to be a major source of qubit decoherence at millikelvin temperatures. In addition to Al, Nb is a commonly used metallization layer in superconducting qubits. Consequently, a significant effort is required to develop and qualify processes that mitigate defects in Nb films. As the fabrication of complete superconducting qubits and their characterization at millikelvin temperatures is a time and resource intensive process, it is desirable to have measurement tools that can rapidly characterize the properties of films and evaluate different treatments. Here, we show that measurements of the variation of the superconducting critical temperature Tc with an applied external magnetic field H (of the phase boundary T c - H) performed with very high-resolution show features that are directly correlated with the structure of the Nb films. In combination with x-ray diffraction measurements, we show that one can even distinguish variations in the size and crystal orientation of the grains in a Nb film by small but reproducible changes in the measured superconducting phase boundary.
Original language | English (US) |
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Article number | 202601 |
Journal | Applied Physics Letters |
Volume | 121 |
Issue number | 20 |
DOIs | |
State | Published - Nov 14 2022 |
Funding
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 No. DEAC02-07CH11359. This work made use of the NUFAB facility of Northwestern University's NUANCE Center, which has received support from the SHyNE Resource (No. NSF ECCS-2025633), the IIN, and Northwestern's MRSEC program (No. NSF DMR-1720139). This work made use of the Jerome B. Cohen X-ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (No. DMR-1720139) at the Materials Research Center of Northwestern University and the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (No. NSF ECCS-2025633). Additional support and equipment were provided by the U.S. Office of Naval Research through a Defense University Research Instrumentation Program (DURIP) under Grant No. W911NF-20-1-0066.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)