Low-temperature dynamics of insulating glasses is dominated by a macroscopic concentration of tunneling two-level systems (TTLS). The distribution of the switching/relaxation rates of TTLS is exponentially broad, which results in a nonequilibrium state of the glass at arbitrarily long time scales. Due to the electric dipolar nature, the switching TTLS generate fluctuating electromagnetic fields. We study the effect of the nonthermal slow fluctuators on the dephasing of a solid-state qubit. We find that at low enough temperatures nonstationary contribution can dominate the stationary (thermal) one, and we discuss how this effect can be minimized.

• Received 10 April 2006

DOI:https://doi.org/10.1103/PhysRevB.73.180201