Archan Banerjee

Performance of Superconducting Resonators Suspended on SiN Membranes

  1. Trevor Chistolini,
  2. Kyunghoon Lee,
  3. Archan Banerjee,
  4. Mohammed Alghadeer,
  5. Christian Jünger,
  6. M. Virginia P. Altoé,
  7. Chengyu Song,
  8. Sudi Chen,
  9. Feng Wang,
  10. David I. Santiago,
  11. and Irfan Siddiqi
Correlated errors in superconducting circuits due to nonequilibrium quasiparticles are a notable concern in efforts to achieve fault tolerant quantum computing. The propagation of quasiparticles
causing these correlated errors can potentially be mediated by phonons in the substrate. Therefore, methods that decouple devices from the substrate are possible solutions, such as isolating devices atop SiN membranes. In this work, we validate the compatibility of SiN membrane technology with high quality superconducting circuits, adding the technique to the community’s fabrication toolbox. We do so by fabricating superconducting coplanar waveguide resonators entirely atop a thin (∼110 nm) SiN layer, where the bulk Si originally supporting it has been etched away, achieving a suspended membrane where the shortest length to its thickness yields an aspect ratio of approximately 7.4×103. We compare these membrane resonators to on-substrate resonators on the same chip, finding similar internal quality factors ∼105 at single photon levels. Furthermore, we confirm that these membranes do not adversely affect the resonator thermalization rate. With these important benchmarks validated, this technique can be extended to qubits.
arxiv pdf

Localization and reduction of superconducting quantum coherent circuit losses

  1. M. Virginia P. Altoé,
  2. Archan Banerjee,
  3. Cassidy Berk,
  4. Ahmed Hajr,
  5. Adam Schwartzberg,
  6. Chengyu Song,
  7. Mohammed Al Ghadeer,
  8. Shaul Aloni,
  9. Michael J. Elowson,
  10. John Mark Kreikebaum,
  11. Ed K. Wong,
  12. Sinead Griffin,
  13. Saleem Rao,
  14. Alexander Weber-Bargioni,
  15. Andrew M. Minor,
  16. David I. Santiago,
  17. Stefano Cabrini,
  18. Irfan Siddiqi,
  19. and D. Frank Ogletree
Quantum sensing and computation can be realized with superconducting microwave circuits. Qubits are engineered quantum systems of capacitors and inductors with non-linear Josephson
junctions. They operate in the single-excitation quantum regime, photons of 27μeV at 6.5 GHz. Quantum coherence is fundamentally limited by materials defects, in particular atomic-scale parasitic two-level systems (TLS) in amorphous dielectrics at circuit interfaces.[1] The electric fields driving oscillating charges in quantum circuits resonantly couple to TLS, producing phase noise and dissipation. We use coplanar niobium-on-silicon superconducting resonators to probe decoherence in quantum circuits. By selectively modifying interface dielectrics, we show that most TLS losses come from the silicon surface oxide, and most non-TLS losses are distributed throughout the niobium surface oxide. Through post-fabrication interface modification we reduced TLS losses by 85% and non-TLS losses by 72%, obtaining record single-photon resonator quality factors above 5 million and approaching a regime where non-TLS losses are dominant. [1]Müller, C., Cole, J. H. & Lisenfeld, J. Towards understanding two-level-systems in amorphous solids: insights from quantum circuits. Rep. Prog. Phys. 82, 124501 (2019)
arxiv pdf