The properties of a quantum material are driven by links between its electrons known as quantum correlations. A RIKEN researcher has shown mathematically that, at non-zero temperatures, these connections can only exist over very short distances when more than two particles are involved. This finding, now published in Physical Review X, sets a fundamental limit on just how “exotic” a quantum material can be under realistic, finite-temperature conditions.

A fascinating aspect of quantum physics is the concept that two particles that are spatially separated can communicate with each other. This so-called “spooky action at a distance,” as Einstein referred to it, is crucial for understanding the origin of the exotic properties that arise in some materials, particularly at low temperatures.

These unusual material properties are determined by the exact nature of the quantum correlation, and the material is said to be in a specific quantum phase. This is analogous to the traditional phases of matter—solid, liquid, and gas—being defined by the chemical interactions between the atoms.