Intrinsic Multi-Mode Interference for Passive Suppression of Purcell Decay in Superconducting Circuits

  1. Mustafa Bakr,
  2. Mohammed Alghadeer,
  3. Simon Pettersson Fors,
  4. Simone D. Fasciati,
  5. Shuxiang Cao,
  6. Atharv Mahajan,
  7. Smain Amari,
  8. Anton Frisk Kockum,
  9. and Peter Leek
Decoherence due to radiative decay remains an important consideration in scaling superconducting quantum processors. We introduce a passive, interference-based methodology for suppressing radiative decay using only the intrinsic multi-mode structured environment of superconducting circuits. By taking into account the full electromagnetic mode-mode couplings within the device, we derive analytic conditions that enable destructive interference. These conditions are realized by introducing controlled geometric asymmetries — such as localized perturbations to the transmon capacitor — which increase mode hybridization and activate interference between multiple decay pathways. We validate this methodology using perturbation theory, full-wave electromagnetic simulations, and experimental measurements of a symmetry-broken transmon qubit with improved coherence times.
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