The two TLS model where we are where are we going

The generic existence of two level systems TLSs in amorphous systems was postulated long ago to explain the intruiging universality of their low temperature properties Although their nature is not yet understood these TLSs are used to explain a wide range of phenomena including 1 f noise and superconducting qubit decoherence Recently we have suggested that two types of TLSs exist distinct by their symmetry under local inversion This model allows for the explanation of some long standing questions such as quantitative universality of phonon attenuation propertie