When the gamma ray photon hits the SPP condensate the SPPs blockade the gamma ray from a frequency above that that exists globally in the condensate.
See http://arxiv.org/pdf/1206.0944v2.pdf The quantum theory of photodetection and optical coherence as originally formulated by Glauber [1] is central to all of quantum optics and has occupied a key role in understanding radiation-matter interactions. Photodetection is also common to quantum-state engineering [2] and quantum information protocols [3]. One of the most prominent effects that shows nonclassical behavior of a quantum emitter is a phenomenon known as photon blockade [4{6], where a coherent excitation of a cavity coupled to a highly nonlinear quantum system, such as a single atom, quantum dot or superconducting qubit, generates an output train of single photons. This photon statistics for the cavity output can be investigated by measuring the intensity correlation function g(2)( ), which demonstrates the nonclassical character of the transmitted field.
