Symmetry protected single photon subradiance
  We study the protection of subradiant states by the symmetry of the atomic distributions in the Dicke limit, in which collective Lamb shifts cannot be neglected. We find that anti-symmetric states are subradiant states for distributions with reflection symmetry. Continuous symmetry can also be used to achieve subradiance. This study is relevant to the problem of robust quantum memory with long storage time and fast readout. 
Han Cai, Da-Wei Wang, Anatoly A. Svidzinsky, Shi-Yao Zhu and Marlan O.   Scully
physics.optics quant-ph