What did the US have in the Potsdam Conference that they didn't have in the Yalta Conference?

At the Potsdam Conference, the United States had successfully tested its first atomic bomb, which provided them with a significant military advantage and a stronger bargaining position in negotiations with the Allies. This development allowed the U.S. to exert more influence over post-war arrangements in Europe and the Pacific. In contrast, at the Yalta Conference, the U.S. was still in the process of planning the use of atomic energy and lacked this critical leverage.