There is little doubt that the Defense Department needs help from Silicon Valley’s biggest companies as it pursues work on artificial intelligence. The question is whether the people who work at those companies are willing to cooperate. Robert Work, a former deputy secretary of defense, announced last week that he is teaming up with the Center for a New American Security, an influential Washington think tank that specializes in national security, to create a task force of former government officials, academics and representatives from private industry.