We have developed a method for extracting the high-frequency noise spectral density of an rf-SQUID flux qubit from macroscopic resonant tunneling (MRT) rate measurements. The extracted noise spectral density is consistent with that of an ohmic environment up to frequencies ~ 4 GHz. We have also derived an expression for the MRT lineshape expected for a noise spectral density consisting of such a broadband ohmic component and an additional strongly peaked low-frequency component. This hybrid model provides an excellent fit to experimental data across a range of tunneling amplitudes and temperatures.
@article{arxiv.1103.1931,
title = {Probing High Frequency Noise with Macroscopic Resonant Tunneling},
author = {T. Lanting and M. H. S. Amin and M. W. Johnson and F. Altomare and A. J. Berkley and S. Gildert and R. Harris and J. Johansson and P. Bunyk and E. Ladizinsky and E. Tolkacheva and D. V. Averin},
journal= {arXiv preprint arXiv:1103.1931},
year = {2011}
}