Temperature Dependence of the Energy Relaxation Rate in an RF-SQUID Flux Qubit

From microwave and resonant tunneling spectroscopy measurements we independently obtained all device parameters needed to reconstruct the Hamiltonian of an RF-SQUID flux qubit. Energy relaxation of the qubit as a function of flux bias and temperature was investigated experimentally. It is found that the energy relaxation rate at different flux biases scales to a universal temperature dependence. This universal T-dependence of T₁ time agrees well with a theoretical model in which the thermal equilibrium population of the excited states is considered.