Why Study Noise due to Two Level Systems: A Suggestion for   Experimentalists
  Noise is often considered to be a nuisance. Here we argue that it can be a useful probe of fluctuating two level systems in glasses. It can be used to: (1) shed light on whether the fluctuations are correlated or independent events; (2) determine if there is a low temperature glass or phase transition among interacting two level systems, and if the hierarchical or droplet model can be used to describe the glassy phase; and (3) find the lower bound of the two level system relaxation rate without going to ultralow temperatures. Finally we point out that understanding noise due to two level systems is important for technological applications such as quantum qubits that use Josephson junctions. 
Clare C. Yu