Experimental characterization of the two current states in a Nb persistent-current qubit

We present experiments to characterize a Nb persistent-current qubit as a two-state system. The magnetization signal from the qubit is read-out by a DC-SQUID with near single-shot efficiency. Experiments varying SQUID ramp-rate and temperature suggest thermal activation occurs between the two circulating current states. Such data can be used to fit the parameters of the system, in order to characterize its performance as a potential quantum bit.