As quantum coherence times of superconducting circuits have increased from nanoseconds to hundreds of microseconds, they are currently one of the leading platforms for quantum information processing. However, coherence needs to further improve by orders of magnitude to reduce the prohibitive hardware overhead of current error correction schemes. Reaching this goal hinges on reducing the density of broken Cooper pairs, so-called quasiparticles. Here, we show that environmental radioactivity is a significant source of nonequilibrium quasiparticles. Moreover, ionizing radiation introduces time-correlated quasiparticle bursts in resonators on the same chip, further complicating quantum error correction. Operating in a deep-underground lead-shielded cryostat decreases the quasiparticle burst rate by a factor fifty and reduces dissipation up to a factor four, showcasing the importance of radiation abatement in future solid-state quantum hardware.
@article{arxiv.2005.02286,
title = {Reducing the impact of radioactivity on quantum circuits in a deep-underground facility},
author = {Laura Cardani and Francesco Valenti and Nicola Casali and Gianluigi Catelani and Thibault Charpentier and Massimiliano Clemenza and Ivan Colantoni and Angelo Cruciani and Luca Gironi and Lukas Grünhaupt and Daria Gusenkova and Fabio Henriques and Marc Lagoin and Maria Martinez and Giorgio Pettinari and Claudia Rusconi and Oliver Sander and Alexey V. Ustinov and Marc Weber and Wolfgang Wernsdorfer and Marco Vignati and Stefano Pirro and Ioan M. Pop},
journal= {arXiv preprint arXiv:2005.02286},
year = {2021}
}