Entanglement of macroscopically distinct states of light. (arXiv:1811.01041v3 [quant-ph] UPDATED)

Schr\"odinger's famous Gedankenexperiment has inspired multiple generations
of physicists to think about apparent paradoxes that arise when the logic of
quantum physics is applied to macroscopic objects. The development of quantum
technologies enabled us to produce physical analogues of Schr\"odinger's cats,
such as superpositions of macroscopically distinct states as well as entangled
states of microscopic and macroscopic entities. Here we take one step further
and prepare an optical state which, in Schr\"odinger's language, is equivalent
to a superposition of two cats, one of which is dead and the other alive, but
it is not known in which state each individual cat is. Specifically, the alive
and dead states are, respectively, the displaced single photon and displaced
vacuum (coherent state), with the magnitude of displacement being on a scale of
$10^8$ photons. These two states have significantly different photon statistics
and are therefore macroscopically distinguishable.