| Abstract: | Tunneling two-level systems (TLSs) are generic to amorphous systems. At low temperatures TLS tunneling cause 1/f noise, slow relaxation, and most remarkably quantitative universality in all properties related to phonon attenuation. This latter phenomenon is seen equally well in disordered lattices, the archetypal of which is KBr:CN. Here we show that in KBr:CN TLSs have a bimodal distribution of their coupling to the lattice, with the weakly interacting TLSs dominating the density of states at low energies. We then use these characteristics to derive universality. Based on the equivallence of the universal phenomena in disordered lattices and amorphous solids, it is probable that our results can be carried through to the amorphous solids. As such, they may be relevant to the explanation of recent experimental findings regarding the decoherence of superconducting qubits by TLSs, and the relaxation of single TLSs as were first measured via their interaction with the superconducting qubits. |
