Inverse Drexhage effect in Epsilon-Near-Zero Substrates

The Drexhage effect, caused by interference between a dipole and its image formed in a substrate, modifies the local density of optical states of quantum emitters which can either enhance or suppress their spontaneous emission rate depending on the dipole orientation and distance from the substrate. Here, we show that for an epsilon-near-zero (ENZ) substrate, the observed orientation and distance dependence of the spontaneous emission rate is reversed compared to metals. This inverse Drexhage effect is studied for ideal ENZ and real ENZ substrates compared with ideal and real metallic substrates. ENZ metamaterials consisting of a subwavelength metal-dielectric stack are shown to exhibit the conventional Drexhage effects due to the large optical losses associated with these materials. Our results could find applications in quantum sensing, quantum information, and energy-efficient optoelectronic devices.