Suppression of quasiparticle poisoning in transmon qubits by gap engineering

TL;DR

This paper demonstrates that gap engineering in Al-based transmon qubits effectively suppresses quasiparticle tunneling, significantly reducing decoherence and improving qubit stability for superconducting quantum computing.

Contribution

The study introduces a practical gap engineering method to suppress quasiparticle tunneling in transmon qubits, enhancing their coherence and stability.

Findings

Charge parity preserved over 1000 seconds

Reduced qubit energy relaxation rates

Suppressed quasiparticle tunneling significantly

Abstract

The performance of various superconducting devices operating at ultra-low temperatures is impaired by the presence of non-equilibrium quasiparticles. Inelastic quasiparticle (QP) tunneling across Josephson junctions in superconducting qubits results in decoherence and spurious excitations and, notably, can trigger correlated errors that severely impede quantum error correction. In this work, we use "gap engineering" to suppress the tunneling of low-energy quasiparticles in Al-based transmon qubits, a leading building block for superconducting quantum processors. By implementing potential barriers for QP, we strongly suppress QP tunneling across the junction and preserve charge parity for over $10^3$ seconds. The suppression of QP tunneling also results in a reduction in the qubit energy relaxation rates. The demonstrated approach to gap engineering can be easily implemented in all Al-based circuits with Josephson junctions.