Three voices merging into a single chord. That is one way to describe what happens in three layers of graphene when they are placed in a strong magnetic field and cooled to near absolute zero. Each layer contains electrons and 'holes'—empty spots where an electron is missing. Normally, they move independently. But under certain conditions, an electron from one layer and a hole from another bind into a pair, and all such pairs begin to flow together without resistance. This is called an excitonic condensate—a collective state of electron-hole pairs flowing without resistance.

Previously, such a state had only been seen in two layers. Now, Chinese physicists have assembled a 'sandwich' of three graphene layers separated by thin spacers. On top, they placed a layer of tungsten disulfide, which acts as a sensor: it senses charge in the adjacent layers and reports what is happening inside. The sensor showed that when electric fields are tuned, all three layers begin to behave as a single entity. Intermediate energy values indicate that this is not just three separate pairs, but a single three-component state.

This discovery allows for the construction of more complex quantum systems with programmable properties. New layers can be added and their interactions tuned to simulate exotic phases of matter. Three voices in a chord are now not just a metaphor, but real physics.