Topologically protected strongly-correlated states of photons

Understand

Hybrid photonic nanostructures allow the engineering of novel interesting states of light.

• One recent example is topological photonic crystals where a nontrivial Berry phase of the photonic band structure gives rise to topologically protected unidirectionally-propagating (chiral) edge states of photons.
• Here we demonstrate that by coupling an array of emitters to the chiral photonic edge state one can create strongly correlated states of photons in a highly controllable way.
• These are topologically protected and have a number of remarkable universal properties: The outcome of scattering does not depend on the positions of emitters and is given only by universal numbers, the zeroes of Laguerre polynomials; two-photon correlation functions manifest a well-pronounced even-odd effect with respect to the number of emitters, and the result of scattering is robust with respect to fluctuations in the emitters' transition frequencies.