We constructed a cavity QED system with a diamagnetic atom of 171Yb and performed projective measurements on a single nuclear spin. Since Yb has no electronic spin and has 1/2 nuclear spin, the procedure of spin polarization and state verification can be dramatically simplified compared with the pseudo spin-1/2 system. By enhancing the photon emission rate of the 1S0-3P1 transition, projective measurement is implemented for an atom with the measurement time of T_meas = 30us. Unwanted spin flip as well as dark counts of the detector lead to systematic error when the present technique is applied for the determination of diagonal elements of an unknown spin state, which is delta|beta|^2 < 2 * 10^-2. Fast measurement on a long-lived qubit is key to the realization of large-scale one-way quantum computing.
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