Sercan Deve

Evidence for unexpectedly low quasiparticle generation rates across Josephson junctions of driven superconducting qubits

  1. Byoung-moo Ann,
  2. Sang-Jun Choi,
  3. Hee Chul Park,
  4. Sercan Deve,
  5. Robin Dekker,
  6. Gary A. Steele,
  7. Jaseung Ku,
  8. Seung-Bo Shim,
  9. and Junho Suh
Microwave drives applied to superconducting qubits (SCQs) are central to high-fidelity control and fast readout. However, recent studies find that even drives far below the superconducting
gap frequency may cause drive-induced quasiparticle generation (QPG) across Josephson junctions (JJs), posing a serious concern for fault-tolerant superconducting quantum computing. Here, we find experimental evidence that the actual QPG rates in strongly driven SCQs are remarkably lower than expected. We apply intense drive fields through readout resonators, reaching effective qubit drive amplitudes up to 300 GHz. The nonlinear response of the resonators enables quantification of the energy loss from SCQs into their environments, including the contribution from QPG. Even when conservatively attributing all measured dissipation to QPG, the observed energy dissipation rates are far lower than expected from the ideal QPG model. Meanwhile, calculations incorporating high-frequency cutoffs (HFCs) near 17-20 GHz in the QPG conductance can explain the experiments. These HFCs yield QPG rates a few orders of magnitude smaller than those without HFCs, providing evidence that the QPG rates are lower than predicted by the ideal model. Our findings prevent overestimation of drive-induced QPG and provide crucial guidance for operating superconducting quantum processors. Identifying the microscopic origin of the discrepancy opens new material and device opportunities to further mitigate QPG.
arxiv pdf

Resolving non-perturbative renormalization of a microwave-dressed weakly anharmonic superconducting qubit

  1. Byoung-moo Ann,
  2. Sercan Deve,
  3. and Gary A. Steele
Microwave driving is a ubiquitous technique for superconducting qubits (SCQs), but the dressed states description based on the conventionally used perturbation theory and rotating wave
approximation cannot fully capture the dynamics in the strong driving limit. Comprehensive experimental works beyond these approximations applicable for transmons is unfortunately rare, which receive rising interests in quantum technologies. In this work, we investigate a microwave-dressed transmon over a wide range of driving parameters. We find significant renormalization of Rabi frequencies, energy relaxation times, and the coupling rates with a readout resonator, all of which are not quantified without breaking the conventional approximations. We also establish a concise non-Floquet theory beyond the two-state model while dramatically minimizing the approximations, which excellently quantifies the experiments. This work expands our fundamental understanding of time-periodically driven systems and will have an important role in accurately estimating the dynamics of weakly anharmonic qubits. Furthermore, our non-Floquet approach is beneficial for theoretical analysis since one can avoid additional efforts such as the choice of proper Floquet modes, which is more complicated for multi-level systems.
arxiv pdf