the paper is this one, I suppose http://arxiv.org/abs/quant-ph/0302179
it was expected that the vacuum behaves as a noisy channel http://arxiv.org/abs/quant-ph/0301065 and in general entanglements are sensible to Lorentzian boosts (but not much) http://arxiv.org/abs/quant-ph/0302095 http://arxiv.org/abs/quant-ph/0205179 and unforfutanely quantum entropy/information is not a Lorentz covariant concept http://arxiv.org/abs/quant-ph/0212023 bbbut, and this are the good news, there are detailed papers (J. Hardy) about the possibility of entanglement between 'usual' quantum states and 'vacuum' states, like i.e. psi = m |1,a>|0,b> + n |0,a>|1,b> + p |0,a>|0,b> where |1,a> and |0,a> are one-particle and vacuum state directed to a-lice and |1,b> and |0,b> ... directed to b-ob
