I don't know if the following is what you need:What is the biggest object that has been put into a state of superpoition? Wasn't it just barely visiible to the naked eye? Is it sufficiently different from a cat to be an exception to quantum mechanical rules?
U. Delić et al., Science
Cooling of a levitated nanoparticle to the motional quantum ground state
"Quantum control of complex objects in the regime of large size and mass provides opportunities for sensing applications and tests of fundamental physics. The realization of such extreme quantum states of matter remains a major challenge. We demonstrate a quantum interface that combines optical trapping of solids with cavity-mediated light matter interaction. Precise control over the frequency and position of the trap laser with respect to the optical cavity allows us to laser-cool an optically trapped nanoparticle into its quantum ground state of motion from room temperature. The particle comprises of ##10^8## atoms, similar to current Bose-Einstein condensates, with the density of a solid object. Our cooling, in combination with optical trap manipulation, may enable otherwise unachievable superposition states involving large masses."
Can conclusions obtained in experiments with such systems be extended to cat-size objects? Opinions on the results of unperformed experiments may differ.