Protecting superconducting qubits from external sources of loss and heat

TL;DR

Embedding superconducting qubits in an absorptive medium significantly reduces external radiation effects, leading to improved qubit temperature and relaxation times, highlighting external radiation as a key factor in qubit coherence.

Contribution

This study demonstrates a method to enhance superconducting qubit coherence by embedding them in an absorptive medium, reducing external radiation-induced dissipation.

Findings

Effective qubit temperature improved after embedding.

Relaxation time increased over tenfold to 5.7 μs.

External radiation limits qubit coherence, not thermal photons.

Abstract

We characterize a superconducting qubit before and after embedding it along with its package in an absorptive medium. We observe a drastic improvement in the effective qubit temperature and over a tenfold improvement in the relaxation time up to 5.7 $\mu$s. Our results suggest the presence of external radiation inside the cryogenic apparatus can be a limiting factor for both qubit initialization and coherence. We infer from simple calculations that relaxation is not limited by thermal photons in the sample prior to embedding, but by dissipation arising from quasiparticle generation.