Shrinking this down to just 1 qubit is therefore a significant advance. Goswami and co exploit a way of representing the state space of a quantum system as a geometric globe, known as a Bloch sphere. They then represent the location of cities as quantum states on a Bloch sphere. So the process of travelling from one city to the next can be achieved through a series of rotations of the sphere.

In fact, it is possible for the sphere to represent the routes from each city to all the others by the process of superposition. “We use the superposition of states to travel through multiple paths at once,” they say. It is then possible to select the optimal route by through the appropriate measurement of the quantum state.