Highly efficient single photon detectors are ubiquitous in quantum optics and atomic physics. However, many of the theories of single photon detection still arise from the Glauber theory of photodetection which was primarily developed for inefficient detectors (weak light-matter coupling). The first goal of the talk is to contrast the photon counting mechanism in photomultiplier tubes (PMTs), single photon avalanche diodes (SPADs), single electron transistor based photodetectors (SET-PDs) and superconducting nanowire single photon detectors (SNSPDs). This can help develop a general model for single photon detection beyond Glauber's theory.
Secondly, we will present experimental results on time-correlated single photon counting experiments that demonstrate long range dipole-dipole interactions between quantum emitters mediated by metamaterials. We will discuss a fundamental limit to the efficiency of energy transfer between quantum emitters and discuss routes to achieve this limit through induced coherence. Our approach to engineering dipole-dipole interactions can motivate experiments from atomic systems (eg: Rydberg blockade) to biochemistry (Forster/Dexter resonance energy transfer).