Emergence of quantum correlations from interacting fibre-cavity polaritons. G. Muñoz-Matutano, A. Wood, M. Johnson, X. Vidal Asensio, B. Baragiola, A. Reinhard, A. Lemaître, J. Bloch, A. Amo, B. Besga, M. Richard and T. Volz in Nature Mater. 18:213-218 (2019).