An ion is a charged atom. Here we see two of them:
a calcium and a strontium ion. They are superb controllable quantum systems, and we’ll see we can store information into either one. Suppose our strontium is initially in state zero. We can apply a pulse of energy to switch it to state one. Later, for readout, we can use a laser that would have no effect on state zero, but our ion in state one will absorb energy and then emit it back as a photon, a particle of light which we can detect. Let’s zoom out. We see gold strips below. These produce electric fields holding our ions still without physically touching them, and again we see a laser causing an ion to become excited and emit its photon. Zooming out further we see the gold strips are part of a small chip called an ion trap, and then we see surrounding electrical and cooling systems. A final zoom reveals the entire system is encased in a vacuum chamber, which protects it from the atmosphere. Surrounding the vacuum chamber are laser systems, field coils and crucially a photonic link system to capture the photons into an optical fiber. This complete module is a small quantum processor, but now consider two linked modules. When photons meet at the entangler unit in the middle, the ions that created those photons become quantum entangled and so the two modules combine as a single quantum machine. Extending this idea we can have an entire array of modules. We can switch connections so that a module links either to a nearby neighbour or to another far away. In this way we can have a highly connected and scalable quantum brain.