Generation of macroscopic singlet states in a cold atomic ensemble
  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. 
N. Behbood, F. Martin Ciurana, G. Colangelo, M. Napolitano, Geza Toth,   R.J. Sewell and M.W. Mitchell
quant-ph