  Unconventional photon blockade refers to the suppression of multi-photon
states in weakly nonlinear optical resonators via the destructive interference
of different excitation pathways. It has been studied in a pair of coupled
nonlinear resonators and other few-mode systems. Here, we show that
unconventional photon blockade can be greatly enhanced in a chain of coupled
resonators. Specifically, the strength of the nonlinearity in each resonator
needed to achieve unconventional photon blockade is suppressed exponentially
with lattice size. The analytic derivation, based on a weak drive
approximation, is validated by wavefunction Monte Carlo simulations. These
findings show that customized lattices of coupled resonators can be powerful
tools for controlling multi-photon quantum states.
