Measurement results of sample qubit a. (a) Qubit signal. The qubit signal appears as a small shift of the readout SQUID critical current modulation curve, marked by two black dash lines and two arrows. (b) Energy spectrum by applying qubit flux bias with mw/flux bias line. The red dash line is a fit of the spectrum line. (c) Rabi oscillation of the sample, red dots are data.The decay rate of the oscillation is 1.96 μs, extracted by fitting the data with an exponential decay sinusoidal curve (blue curve on the plot), P is the switching probability of the readout SQUID.