

Yesterday you decided to go for a quick drink with friends. One drink turns into one (or several) too many and the next thing you know you've woken up on your floor surrounded by cold pizza and a phone full of texts you should never have sent. Most people have memories of nights like this, but not many people have memories of their walk home. I would like to speak about the quantum random walk: the quantum analogue of the drunk man's walk home. After enough beers it's often the case that we end up in some strange positions. Unfortunately though, it's never possible that we can be in two places at once. So, instead, imagine that some friends all leave the bar together, in one single group. How would the group, as a whole, travel? Would it remain as a tight, compact group or would it spread and be in multiple places at the same time? What happens if someone becomes more interested in the local kebab shop or phone signal is lost and they can no longer contact each other? How do all these different factors affect the walk? Physically, quantum random walks have applications within quantum computation, search algorithms and cryptography. In general, understanding the features of a quantum walk, and determining the control that we need to have on them, can offer a significant advantage over classical methods within computation and security.