One can be an atheist and a Buddhist at the same time, if being atheist just means rejecting the concept of an almighty, all compassionate, creator God. But if you mean rejecting swarga(higher realms), niraya(lower realms) and Samsaric existences, you can't really be called a Buddhist as you are rejecting the teachings of the Buddha. But you can still practice Buddhism.

One can be an atheist and a Buddhist at the same time, if being atheist just means rejecting the concept of an almighty, all compassionate, creator God. But if you mean rejecting swarga(higher realms), niraya(lower realms) and Samsaric existences, you can't really be called a Buddhist as you are rejecting the teachings of the Buddha. But you can still practice Buddhism at a certain level.