Protecting Superconducting Qubits from Quasiparticle Bursts with Phononic Filters*

The investigation and mitigation of decoherence mechanisms in superconducting qubits is critical for the development of superconducting quantum computers. One known source of decoherence is quasiparticle tunneling in Josephson junctions [1]. Experiments have demonstrated the generation of quasiparticles can in part be attributed to ionizing radiation interacting with the sample substrate and producing high energy phonons capable of breaking cooper pairs [2,3]. The isolation of qubits from such phonons could enable the suppression of this decoherence mechanism. To investigate this we design, fabricate, and measure transmon qubits on nanomechanical resonators acting as acoustic low-pass filters. This allows us to study phonon-induced quasiparticle generation rates of on-chip acoustically shielded qubits. We anticipate this technique to be beneficial towards the development of highly coherent superconducting qubits and large scale qubit arrays.

[1]: G. Catelani, S. E. Nigg, S. M. Girvin, R. J. Schoelkopf, and L. I. Glazman. Phys. Rev. B 86, 184514 (2012)

[2]: McEwen, M., Faoro, L., Arya, K. et al. Resolving catastrophic error bursts from cosmic rays in large arrays of superconducting qubits. Nat. Phys. 18, 107–111 (2022).

[3]: Vepsäläinen, A.P., Karamlou, A.H., Orrell, J.L. et al. Impact of ionizing radiation on superconducting qubit coherence. Nature 584, 551–556 (2020).