Properties of two level systems in current-carrying superconductors

Abstract

We show that in disordered superconductors, at sufficiently low frequencies $\omega$, the coupling of TLS to external ac electric fields increases dramatically in the presence of a dc supercurrent. This giant enhancement manifests in all ac linear and nonlinear phenomena. In particular, it leads to a parametric enhancement of the real part of the ac conductivity and, consequently, of the equilibrium current fluctuations. If the distribution of TLS relaxation times is broad, the conductivity is inversely proportional to $\omega$, and the spectrum of the equilibrium current fluctuations takes the form of 1/f noise.

References in corpus (8)

• 1/f noise: implications for solid-state quantum information
• Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits
• Model for l/f Flux Noise in SQUIDs and Qubits
• Microscopic origin of low frequency flux noise in Josephson circuits
• Two-level systems in superconducting quantum devices due to trapped quasiparticles
• One- and two-photon spectroscopy of a flux qubit coupled to a microscopic defect
• Observation of giant two-level systems in a granular superconductor
• Near-power-law temperature dependence of the superfluid stiffness in strongly disordered superconductors