Suppression of photon shot noise dephasing in a tunable coupling superconducting qubit

We report on the suppression of photon shot noise dephasing in a tunable coupling qubit (TCQ). This is achieved by eliminating the dispersive coupling rate, $\chi$, between the TCQ and the readout cavity. We observe that the coherence time approaches twice the relaxation time and becomes less sensitive to thermal photon noise when $\chi$ is tuned close to zero. Experimental results of tunable $\chi$ and its impact on qubit coherence will be presented.