Towards phononic shielding of superconducting qubits

With the recent demonstration of quantum error correction, superconducting qubit platforms have evolved from emerging technologies into scalable industrial architectures. However, achieving full fault tolerance remains limited by qubit lifetimes and correlated noise sources. Among these, mechanically induced decoherence, originating from the cryocooler’s vibrations, has recently emerged as a challenge that can undermine error-correction schemes [1].

Phononic shielding has been shown to enhance qubit [2] or TLS [3] relaxation times. However, integrating such shielding directly into the qubit substrate promises further improvements in coherence while preserving fabrication simplicity.

We present progress toward the realization of a phononic crystal engineered within a silicon substrate through spatial modulation of its density profile at GHz frequencies. By wafer bonding this structured layer onto a secondary support wafer, we create a buried phononic shield that suppresses the propagation of undesired vibrational modes. Superconducting qubits can then be fabricated on the surface using standard processes while preserving their intrinsic coherence. This approach offers a path to mitigate mechanically mediated decoherence and enhance the scalability of superconducting quantum processors.

[1] S. Kono, et al., Nature Communications 15, 3950 (2024)

[2] M. Odeh, et al., Nature Physics, 21, 406–411 (2025)

[3] M. Chen et al. ,Science  Advances .10, 6240 (2024)