To Be or Not to Be a Pair: Giant Molecules in a Quantum Superposition

In human relationships, the question of being a couple or not has a yes-or-no answer: either one is a couple or not. Quantum physics offers an interesting alternative. There, the couples are pairs of atoms that are held together by binding forces to form molecules. Quantum mechanics allows another loophole: a superpostion of free and bound state, where the two atoms are bound and free at the same time. Although this is impossible in our classical world, it is a well known property for quantum mechanical states. Such superpositions have now been observed at the University of Stuttgart for weakly bound ultralong-range molecules.