A Theoretical Investigation of Third-Order Optical Susceptibility in Metronidazolium-Picrate Crystal and Its Potential for Quantum Memory Applications.

In this work, we report a theoretical investigation of the third-order nonlinear optical properties of the metronidazolium-picrate salt. The effects of the crystal environment are accounted for by the Iterative Charge Embedding approach, and the electronic calculations are carried out at the DFT (CAM-B3LYP/6-311++G-(d,p)) level. Furthermore, we use the results to parametrize a cavity Quantum Electrodynamics model for a quantum memory based on the Off-Resonant Cascaded Absorption protocol. The system's performance is then simulated via a Lindblad-type master equation that includes realistic decoherence channels. Our results confirm a strong third-order susceptibility (χ) of 3.4 × 10 (m/V) at 532 nm driven by significant charge polarization in the crystal. The quantum memory simulations, initiated with a single-photon Fock state, reveal that protocol fidelity is critically dependent on the cavity quality factor. A peak retrieval fidelity of 84.51% is achieved in the strong coupling regime, which collapses to less than 1% when the system leaves this regime. These findings demonstrate that METPA is a promising material for quantum photonics, where its strong intrinsic electronic properties can be harnessed in engineered cavity Quantum Electrodynamics systems to realize high-fidelity quantum information protocols.