Disentangling Losses in Tantalum Superconducting Circuits

  1. Kevin D. Crowley,
  2. Russell A. McLellan,
  3. Aveek Dutta,
  4. Nana Shumiya,
  5. Alexander P.M. Place,
  6. Xuan Hoang Le,
  7. Youqi Gang,
  8. Trisha Madhavan,
  9. Nishaad Khedkar,
  10. Yiming Cady Feng,
  11. Esha A. Umbarkar,
  12. Xin Gui,
  13. Lila V. H. Rodgers,
  14. Yichen Jia,
  15. Mayer M. Feldman,
  16. Stephen A. Lyon,
  17. Mingzhao Liu,
  18. Robert J. Cava,
  19. Andrew A. Houck,
  20. and Nathalie P. de Leon
Superconducting qubits are a leading system for realizing large scale quantum processors, but overall gate fidelities suffer from coherence times limited by microwave dielectric loss.
Recently discovered tantalum-based qubits exhibit record lifetimes exceeding 0.3 ms. Here we perform systematic, detailed measurements of superconducting tantalum resonators in order to disentangle sources of loss that limit state-of-the-art tantalum devices. By studying the dependence of loss on temperature, microwave photon number, and device geometry, we quantify materials-related losses and observe that the losses are dominated by several types of saturable two level systems (TLSs), with evidence that both surface and bulk related TLSs contribute to loss. Moreover, we show that surface TLSs can be altered with chemical processing. With four different surface conditions, we quantitatively extract the linear absorption associated with different surface TLS sources. Finally, we quantify the impact of the chemical processing at single photon powers, the relevant conditions for qubit device performance. In this regime we measure resonators with internal quality factors ranging from 5 to 15 x 10^6, comparable to the best qubits reported. In these devices the surface and bulk TLS contributions to loss are comparable, showing that systematic improvements in materials on both fronts will be necessary to improve qubit coherence further.

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.