I disagree with the above post; there is no historical evidence to support it. The use of the Atomic Bomb did not contribute to the start of the Cold War; it began because of Soviet attempts to dominate Europe. At the end of World War II, Joseph Stalin stated that
The war against fascism has ended; the war against capitalism has begun.
Immediately after the end of the war, the Soviets refused to withdraw troops from Eastern Europe. Stalin insisted that he needed to occupy the territory as a buffer against future invasions. During the Yalta Conferences President Franklin Roosevelt, sick and dying, agreed to Stalin's demands that Germany would be occupied and that it must pay heavy reparations to the Soviets. At the later Potsdam Conference, President Harry Truman insisted that free elections be held in the countries of Eastern Europe then under Soviet Control. Stalin flatly refused to allow free elections, stating:
A freely elected government in any of these East European countries would be anti-Soviet, and that we cannot allow.
Stalin argued, perhaps insincerely, that only communist governments in Eastern Europe would protect the Soviet Union from future attacks. So great was Stalin's determination that only war would have forced him to abandon his position, and the U.S. and Britain were unwilling to risk war with the Soviet Union at this time. In May, 1945, President Truman stopped all aid from the U.S. to the Soviets and stated that the U.S. would never support any government which was instituted by force. This was the true cause of the Cold War. The Atomic Bomb became a substantial factor in the arms race which dominated the Cold War; but was not in and of itself a factor in its inception.
An interesting side note: it is commonly believed in Japan that the U.S. used the bomb at Hiroshima and Nagasaki to end the war quickly and prevent any further territorial gains by the Soviets in Eurasia. Although the actual reasons for the use of the bomb are subject to debate; this is the opinion of Japanese historians.
The use of the atomic bomb did help to create the tensions that were the basis of the Cold War.
When the US dropped the atomic bombs on Japan, it created a sense of fear in the Soviet Union's leadership. They knew that they were not near to having such a bomb. Because of this, and because of their general suspicions of the West, the Soviets were very worried about protecting themselves from the West. This led to them taking power over all of Eastern Europe. When they did this, the Western Allies became afraid of the Soviets and the Cold War was on.
US use of the atomic bombs helped to scare the Soviets and, thereby, helped to cause the Cold War.