  Optical cat state plays an essential role in quantum computation and quantum
metrology. Here, we experimentally quantify quantum coherence of an optical cat
state by means of relative entropy and l_1 norm of coherence in Fock basis
based on the prepared optical cat state at rubidium D1 line. By transmitting
the optical cat state through a lossy channel, we also demonstrate the
robustness of quantum coherence of optical cat state in the presence of loss,
which is different from the decoherence properties of fidelity and Wigner
function negativity of the optical cat state. Our results confirm that quantum
coherence of optical cat states is robust against loss and pave the way for the
application with optical cat states.
