Mitigation of quasiparticle loss in superconducting qubits by phonon scattering

Abstract

Quantum error correction will be an essential ingredient in realizing fault-tolerant quantum computing. However, most correction schemes rely on the assumption that errors are sufficiently uncorrelated in space and time. In superconducting qubits this assumption is drastically violated in the presence of ionizing radiation, which creates bursts of high energy phonons in the substrate. These phonons can break Cooper-pairs in the superconductor and, thus, create quasiparticles over large areas, consequently reducing qubit coherence across the quantum device in a correlated fashion. A potential mitigation technique is to place large volumes of normal or superconducting metal on the device, capable of reducing the phonon energy to below the superconducting gap of the qubits. To investigate the effectiveness of this method we fabricate a quantum device with four nominally identical nanowire-based transmon qubits. On the device, half of the niobium-titanium-nitride ground plane is replaced with aluminum (Al), which has a significantly lower superconducting gap. We deterministically inject high energy phonons into the substrate by voltage biasing a galvanically isolated Josephson junction. In the presence of the low gap material, we find a factor of 2-5 less degradation in the injection-dependent qubit lifetimes, and observe that undesired excited qubit state population is mitigated by a similar factor. We furthermore turn the Al normal with a magnetic field, finding no change in the phonon-protection. This suggests that the efficacy of the protection in our device is not limited by the size of the superconducting gap in the Al ground plane. Our results provide a promising foundation for protecting superconducting qubit processors against correlated errors from ionizing radiation.

Main: 9 pages, 4 figures. Supp: 10 pages, 6 figures

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Cited by in corpus (13)

• Coexistence of nonequilibrium density and equilibrium energy distribution of quasiparticles in a superconducting qubit
• Resisting high-energy impact events through gap engineering in superconducting qubit arrays
• Phononic bath engineering of a superconducting qubit
• Modeling phonon-mediated quasiparticle poisoning in superconducting qubit arrays
• Blueprint for all-to-all connected superconducting spin qubits
• Cosmic-ray-induced correlated errors in superconducting qubit array
• Heat dissipation mechanisms in hybrid superconductor-semiconductor devices revealed by Joule spectroscopy
• Cosmic muon flux attenuation methods for superconducting qubit experiments
• Modeling Athermal Phonons in Novel Materials using the G4CMP Simulation Toolkit
• Gatemon Qubit Revisited for Improved Reliability and Stability
• Nonclassical radiation from a nonlinear oscillator driven solely by classical $1/f$ noise
• Charge Parity Rates in Transmon Qubits with Different Shunting Capacitors
• Electron-phonon interactions in the Andreev Bound States of aluminum nanobridge Josephson junctions