Restoring Two-Photon Quantum Correlations Using Even-Parity Optimization

High-dimensional quantum entanglement in photons offers significant advantages in quantum technologies, including enhanced information capacity and improved security in communication protocols [1]. However, when entangled photons propagate through complex media-such as turbulent atmospheres or multimode fibers-their spatial correlations degrade, limiting their practical utility [2]. While the effects of disorder near the nonlinear crystal generating entangled photons are well understood [3], the impact of disorder in the far field remains less explored. We have systematically investigated the impact of arbitrary phase distortions in the far field by decomposing the disorder into even- and odd-parity components [4]. Through theoretical analysis, we have demonstrated that only the even-parity component affects two-photon interference, while the odd-parity component leaves photon correlations unchanged, as shown in Fig. 1. To validate this prediction, we used a deformable mirror to introduce controlled phase distortions and experimentally confirm our findings. Additionally, numerical simulations showed that these results hold even for more complex disorders.