  We report the generation of a macroscopic singlet state in a cold atomic
sample via quantum non-demolition (QND) measurement induced spin squeezing. We
observe 3 dB of spin squeezing and detect entanglement of up to $5.5\times10^5
$ atoms with $5\sigma$ statistical significance using a generalized spin
squeezing inequality. The degree of squeezing implies at least 50% of the atoms
have formed singlets, while the response to a magnetic field gradient indicates
entanglement bonds at all length scales, a characteristic of quantum spin
liquids.
