Persistent Entanglement in the Classical Limit
  The apparent difficulty in recovering classical nonlinear dynamics and chaos from standard quantum mechanics has been the subject of a great deal of interest over the last twenty years. For open quantum systems - those coupled to a dissipative environment and/or a measurement device - it has been demonstrated that chaotic-like behaviour can be recovered in the appropriate classical limit. In this paper, we investigate the entanglement generated between two nonlinear oscillators, coupled to each other and to their environment. Entanglement - the inability to factorise coupled quantum systems into their constituent parts - is one of the defining features of quantum mechanics. Indeed, it underpins many of the recent developments in quantum technologies. Here we show that the entanglement characteristics of two `classical' states (chaotic and periodic solutions) differ significantly in the classical limit. In particular, we show that significant levels of entanglement are preserved only in the chaotic-like solutions. 
M.J. Everitt, T.D. Clark, P.B. Stiffell, J.F. Ralph, A.R. Bulsara and   C.J. Harland