Einstein's elevator reveals its quantum secret: the "footprint" of free fall detected

Albert Einstein recalled that the happiest idea of his life came to him in 1907 while thinking about an elevator: if the cables broke and the cabin plunged in free fall, the person trapped inside would float without feeling their own weight. Upon releasing a coin or keys, they would see the objects suspended in the air next to them. Inside that closed box there would be no way to know if one is falling toward the center of the Earth or resting peacefully on a ship drifting through outer space. That equivalence between free fall and the absence of gravity was the seed of general relativity. But what would happen if the one traveling in the elevator is not a person, but a tiny particle that obeys the laws of quantum physics?