  Exceptional points (EPs), singularities of non-Hermitian physics where
complex spectral resonances degenerate, are one of the most exotic features of
nonequilibrium open systems with unique properties. For instance, the emission
rate of quantum emitters placed near resonators with EPs is enhanced (compared
to the free-space emission rate) by a factor that scales quadratically with the
resonance quality factor. Here, we verify the theory of spontaneous emission at
EPs by measuring photoluminescence from photonic-crystal slabs that are
embedded with a high-quantum-yield active material. While our experimental
results verify the theoretically predicted enhancement, it also highlights the
practical limitations on the enhancement due to material loss. Our designed
structures can be used in applications that require enhanced and controlled
emission, such as quantum sensing and imaging.
