The employee, Jian Zhang, joined the Meta Robotics Studio, the social media company confirmed on Tuesday. Separately, three more AI researchers are leaving Apple’s in-house large language models team, adding to upheaval in that group, according to people with knowledge of the matter. The latest string of departures — all taking place over the last week — includes John Peebles, Nan Du and Zhao Meng, said the people, who asked not to be identified because the moves haven’t been announced.