  We report single-shot readout of a superconducting flux qubit by using a
flux-driven Josephson parametric amplifier (JPA). After optimizing the readout
power, gain of the JPA and timing of the data acquisition, we observe the Rabi
oscillations with a contrast of 74% which is mainly limited by the bandwidth of
the JPA and the energy relaxation of the qubit. The observation of quantum
jumps between the qubit eigenstates under continuous monitoring indicates the
nondestructiveness of the readout scheme.
