proof of concept
Technical term used in business, engineering, and research to describe a demonstration that a concept or theory is feasible.
This project is at the proof-of-concept stage.
After the proof of concept, we plan to move to commercialization.
実証実験 is a broader term for a verification experiment, while 概念実証 specifically refers to demonstrating the feasibility of a concept.
Compound of 概念 (concept) and 実証 (proof, verification). Likely a calque from English 'proof of concept'.