We report on an experimental realization of multimaterial dielectric mirror coatings designed through a multi-objective optimization algorithm to simultaneously minimize thermal noise and optical losses. We validate this design strategy by fabricating and characterizing two distinct ternary systems: a ${\mathrm{Si}\mathrm{N}}_x$-based proof of concept and a ${\text{Ti::GeO}}_2$-based system targeting lower optical losses. The performance of the ${\mathrm{Si}\mathrm{N}}_x$ coating shows remarkable agreement with predictions, demonstrating a noise amplitude spectral density reduction of $0.82$ with respect to current reference coatings, and validating our design-to-fabrication pipeline. The ${\text{Ti::GeO}}_2$-based system achieves the crucial goal of sub-parts-per-million absorption; its measured thermal noise, however, is higher than the theoretically predicted level of $0.71$, extrapolated from single-layer material characterization. A dedicated tolerance analysis confirms that this discrepancy is not attributable to random thickness errors, emphasizing that further studies of the manufacturing process are needed to fully exploit this combination of materials. This work establishes a robust method for producing complex, high-performance optical coatings tailored for precision experiments.

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• Light propagation, transmission & absorption
• Noise
• Optical materials & elements
• Optimization problems
• Thermal properties
• Coatings
• Dielectrics
• Gravitational wave detectors
• Sputtering