Cosmic muon flux attenuation methods for superconducting qubit experiments

Abstract

We propose and demonstrate two mitigation methods to attenuate the cosmic muon flux compatible with experiments involving superconducting qubits. Using a specifically-built cosmic muon detector, we find that chips oriented towards the horizon compared to chips looking at the sky overhead experience a decrease of a factor 1.6 of muon counts at the surface. Then, we identify shielded shallow underground sites, ubiquitous in urban environments, where significant additional attenuation, up to a factor 35 for 100-meter depths, can be attained. The two methods here described are the first proposed to directly reduce the effects from cosmic rays on qubits by attenuating the noise source, complementing existing on-chip mitigation strategies. We expect that both on-chip and off-chip methods combined will become ubiquitous in quantum technologies based on superconducting qubit circuits.

Mitigation of Cosmic Rays-Induced Errors in Superconducting Quantum Processors

“…As an example, the cryogenic facility at the Laboratori Nazionali del Gran Sasso (LNGS), in Italy, which is covered by a rock overburden of 1.4 km, provides a reduction factor of about 1 million for the muon flux [26], [27]. Nonetheless, as shown in [8], effective suppression factors can also be achieved in shallower sites (up to a factor of 35 for depths of 100 meter). Fig.…”

“…While environmental radioactivity can be mitigated by using dedicated shielding and radio-pure materials in the proximity of the qubits, benefiting from the experience of the scientific community developing low-radioactivity detectors for Particle Physics, cosmic-ray muons cannot be easily suppressed. Interesting studies have shown that shallow underground sites can provide good attenuation factors, ranging from 2 to a factor of 35 for depths of 10 meters and 100 meters, respectively [8]. In addition, it has been demonstrated in [8] using a specificallybuilt cosmic muon detector that, by orienting chips towards the horizon, the muon flux above-ground can be reduced by a factor of 1.6.…”

“…Interesting studies have shown that shallow underground sites can provide good attenuation factors, ranging from 2 to a factor of 35 for depths of 10 meters and 100 meters, respectively [8]. In addition, it has been demonstrated in [8] using a specificallybuilt cosmic muon detector that, by orienting chips towards the horizon, the muon flux above-ground can be reduced by a factor of 1.6. However, to date, the only method to significantly reduce the muon flux is to operate quantum processors in deep underground laboratories [9], [10].…”