Final answer:
The first experiment to address the Detection Loophole was the Aspect Experiment, conducted in the 1980s, which tested the validity of Bell's theorem in quantum mechanics.
Step-by-step explanation:
The first experiment that addressed the Detection Loophole in Bell tests was the Aspect Experiment. This experiment, conducted in the early 1980s by Alain Aspect and his team, aimed to test the validity of Bell's theorem and was a major advancement in the field of quantum mechanics. Although the Aspect Experiment made significant progress, it did not completely close the Detection Loophole; however, it paved the way for future experiments that sought to address it more thoroughly. The Detection Loophole refers to the problem that, in experiments testing for non-locality or entanglement, not all entangled particle pairs may be detected, potentially biasing the results.