If we turn around, our conversation partner faces our back, only after a full rotation, the original state is restored. With quantum particles, this is different: Sometimes they have to be rotated twice to make sure that they end up in their original state. That may sound strange – but Gerald Badurek, Dean of Physics, explains it with a necktie and tells us what this has to do with quantum computing:

(German, English and Japanese captions are available!)