Observing Non-Markovian Effects of Two-Level Systems in a Niobium Coaxial Resonator with a Single-Photon Lifetime of 10 ms

  1. P. Heidler,
  2. C. M. F. Schneider,
  3. K. Kustura,
  4. C. Gonzalez-Ballestero,
  5. O. Romero-Isart,
  6. and G. Kirchmair
Understanding and mitigating loss channels due to two-level systems (TLS) is one of the main corner stones in the quest of realizing long photon lifetimes in superconducting quantum circuits. Typically, the TLS to which a circuit couples are modelled as a large bath without any coherence. Here we demonstrate that the coherence of TLS has to be considered to accurately describe the ring-down dynamics of a coaxial quarter-waver resonator with an internal quality factor of 0.5×109 at the single-photon level. The transient analysis reveals an effective non-markovian dynamics of the combined TLS and cavity system, which we can accurately fit by introducing a comprehensive TLS model. The fit returns relaxation times around T1=0.8μs for a total of N≈2×108 TLS with power-law distributed coupling strengths. Despite the short-lived TLS excitations, we observe long-term effects on the cavity decay due to coherent elastic scattering between the resonator field and the TLS. The presented method is applicable to various systems and allows for a simple characterization of TLS properties.
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