Following the referee’s suggestion we have added the reference to Mekhov’s paper.
Other examples of many-atom-cavity continuous observation papers: W. Niedenzu, S. Schütz, H. Habibian, G. Morigi, and H. Ritsch, Phys. Rev.  88, 033830 (2013). I. B. Mekhov and H. Ritsch, Phys. Rev. Lett. 102, 020403 (2009). J. F. Corney and G. J. Milburn, Phys. Rev. A 58, 2399 (1998). I. D. Leroux, M. H. Schleier-Smith, and V. Vuletić, Phys. Rev. Lett. 104, 073602 (2010).