Anjali Premkumar

Microscopic Relaxation Channels in Materials for Superconducting Qubits

  1. Anjali Premkumar,
  2. Conan Weiland,
  3. Sooyeon Hwang,
  4. Berthold Jäck,
  5. Alexander P.M. Place,
  6. Iradwikanari Waluyo,
  7. Adrian Hunt,
  8. Valentina Bisogni,
  9. Jonathan Pelliciari,
  10. Andi Barbour,
  11. Mike S. Miller,
  12. Paola Russo,
  13. Fernando Camino,
  14. Kim Kisslinger,
  15. Xiao Tong,
  16. Mark S. Hybertsen,
  17. Andrew A. Houck,
  18. and Ignace Jarrige
Despite mounting evidence that materials imperfections are a major obstacle to practical applications of superconducting qubits, connections between microscopic material properties
and qubit coherence are poorly understood. Here, we perform measurements of transmon qubit relaxation times T1 in parallel with spectroscopy and microscopy of the thin polycrystalline niobium films used in qubit fabrication. By comparing results for films deposited using three techniques, we reveal correlations between T1 and grain size, enhanced oxygen diffusion along grain boundaries, and the concentration of suboxides near the surface. Physical mechanisms connect these microscopic properties to residual surface resistance and T1 through losses arising from the grain boundaries and from defects in the suboxides. Further, experiments show that the residual resistance ratio can be used as a figure of merit for qubit lifetime. This comprehensive approach to understanding qubit decoherence charts a pathway for materials-driven improvements of superconducting qubit performance.
arxiv pdf

New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds

  1. Alex P. M. Place,
  2. Lila V. H. Rodgers,
  3. Pranav Mundada,
  4. Basil M. Smitham,
  5. Mattias Fitzpatrick,
  6. Zhaoqi Leng,
  7. Anjali Premkumar,
  8. Jacob Bryon,
  9. Sara Sussman,
  10. Guangming Cheng,
  11. Trisha Madhavan,
  12. Harshvardhan K. Babla,
  13. Berthold Jäck,
  14. Andras Gyenis,
  15. Nan Yao,
  16. Robert J. Cava,
  17. Nathalie P. de Leon,
  18. and Andrew A. Houck
The superconducting transmon qubit is a leading platform for quantum computing and quantum science. Building large, useful quantum systems based on transmon qubits will require significant
improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that relaxation likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of two-dimensional transmon qubits have remained elusive for several years. Here, we fabricate two-dimensional transmon qubits that have both lifetimes and coherence times with dynamical decoupling exceeding 0.3 milliseconds by replacing niobium with tantalum in the device. We have observed increased lifetimes for seventeen devices, indicating that these material improvements are robust, paving the way for higher gate fidelities in multi-qubit processors.
arxiv pdf