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 μs. 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.
@article{arxiv.1108.1383,
title = {Protecting superconducting qubits from external sources of loss and heat},
author = {Antonio D. Córcoles and Jerry M. Chow and Jay M. Gambetta and Chad Rigetti and J. R. Rozen and George A. Keefe and Mary Beth Rothwell and Mark B. Ketchen and M. Steffen},
journal= {arXiv preprint arXiv:1108.1383},
year = {2011}
}