Suppressing relaxation in superconducting qubits by quasiparticle pumping

TL;DR

This paper introduces a stochastic control method to dynamically shape the noise environment in superconducting qubits, significantly reducing quasiparticle density and enhancing qubit relaxation times and coherence stability.

Contribution

It demonstrates a novel quasiparticle pumping technique that effectively reduces quasiparticle density and improves qubit coherence, addressing irreversible relaxation errors.

Findings

70% reduction in quasiparticle density

Threefold increase in qubit relaxation times

Reduced coherence variability

Abstract

Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. In this work, we investigate a complementary, stochastic approach to reducing errors: instead of deterministically reversing the unwanted qubit evolution, we use control pulses to shape the noise environment dynamically. In the context of superconducting qubits, we implement a pumping sequence to reduce the number of unpaired electrons (quasiparticles) in close proximity to the device. We report a 70% reduction in the quasiparticle density, resulting in a threefold enhancement in qubit relaxation times, and a comparable reduction in coherence variability.