Figure 2. When you throw a ball at a wall, you can be sure it will bounce back at you. You would be extremely surprised if the ball suddenly appeared on the other side of a solid wall. This is exactly the type of phenomenon that has given quantum physics a reputation for being bizarre and unintuitive.

Figure 3. Initially, the experiment has no voltage at all. It is as if there is a lever in the off position, and something is blocking from being moved to on. Without the effects of quantum mechanics, this state would remain unchanged. Suddenly, a voltage appears. This is as if the lever has moved from off to on, despite the barrier between the two. What happened in the experiment is called macroscopic quantum tunnelling.

Figure 5. In a normal conductor, the electrons jostle with each other and with the material. When a material becomes a superconductor, the electrons join up as pairs, Cooper pairs, and form a current where there is no resistance. The gap in the illustration marks the Josephson junction. Cooper pairs can behave as if they were all a single particle that fills the entire electrical circuit. Quantum mechanics describes this collective state using a shared wave function. The properties of this wave function play the leading role in the laureates’ experiment.