Classical vs quantum walk

Both walkers start in the middle and take 80 steps. The gray one does an ordinary random walk (flip a coin, step, flip, step) and spreads into the bell curve you'd expect. The cyan one does a quantum walk, and it does not do what you'd expect: it avoids the middle and piles up in two sharp horns out at the edges, about as far as it could possibly have gotten.

Now drag decoherence. At zero the quantum walker stays weird; turn it up and the weirdness leaks out a step at a time until it's sitting in the same bell curve as the gray one (which is, very roughly, why big warm things like you and me act classical).