Suppression of Correlated Qubit Errors by Silicon Micromachining

Recent work has demonstrated that high-energy particle impacts result in phonon-mediated quasiparticle poisoning and correlated errors in superconducting qubits. This poses a problem for error correction codes, which generally assume uncorrelated errors. In this work, we investigate suppression of these errors by using a deep reactive ion etch process to modify the propagation of pair-breaking phonons in the qubit substrate. We utilize three distinct approaches. In the first, we incorporate an array of scattering centers to suppress ballistic phonon propagation. In the remaining two approaches, we define phonon bottlenecks and moats to acoustically decouple individual qubits from their neighbors. We use direct injection of quasiparticles from SIS junctions arrayed around the chip perimeter to generate a high flux of pair-breaking phonons. We compare the rates of correlated relaxation events and charge-parity switches in these devices to baseline data from devices with no mitigation.