Stochastic models for the kinetics of ensembles of two-level systems

Savino Longo, Domenico Bruno, M. Capitelli +1 more

H. J. Hilhorst, Masuo Suzuki, B. U. Felderhof

Yu. S. Oseledchik, G. A. Miroshnik

Ranko Richert

Nonexponential decay of an ensemble of first-order processes are modeled assuming distributions of rate-controlling parameters to be responsible for dispersive kinetics. Some problems of deriving microscopic properties from experimental decay data are illustrated focusing on hole-burning kinetics on the basis of the two-level system model. This approach is compared with reasonings leading to the logarithmic decay law.

Z. Kanokov

Tamin Tai, Jingnan Cai, Steven M. Anlage

Superconducting resonators are widely used in many applications such as qubit readout for quantum computing, and kinetic inductance detectors. These resonators are susceptible to numerous loss and noise mechanisms, especially the dissipation due to two-level systems (TLS) which become the dominant source of loss in the few-photon and low temperature regime. In this study, capacitively-coupled aluminum half-wavelength coplanar waveguide resonators are investigated. Surprisingly, the loss of the resonators is observed to decrease with a lowering temperature at low excitation powers and temperatures below the TLS saturation. This behavior is attributed to the reduction of the TLS resonant response bandwidth with decreasing temperature and power to below the detuning between the TLS and the resonant photon frequency in a discrete ensemble of TLS. When response bandwidths of TLS are smaller than their detunings from the resonance, the resonant response and thus the loss is reduced. At higher excitation powers, the loss follows a logarithmic power dependence, consistent with predictions from the generalized tunneling model (GTM). A model combining the discrete TLS ensemble with the GTM is proposed and matches the temperature and power dependence of the measured internal loss of the resonator with reasonable parameters.