A research team has developed an exactly solvable model showing how trapped light can generate magnetic order in a one-dimensional spin chain. The study, published in Physical Review Research, examines a classical Ising chain coupled to a single cavity photon mode.
In the conventional one-dimensional Ising model, neighboring magnetic particles do not undergo a magnetic phase transition at finite temperature. Phase transitions can occur in higher-dimensional systems, making the Ising model an important tool for studying collective behavior in interacting particles.
The researchers investigated whether coupling the chain to light could change this behavior. Their model shows that photons confined within a mirror cavity create long-range interactions linking all the spins. These photon-mediated interactions allow the chain to develop magnetic order and a macroscopic electromagnetic field at a specific temperature.
The system undergoes a second-order superradiant phase transition at finite temperature. The team analytically determined the magnetization, photon number and critical temperature, obtaining exact results in the thermodynamic limit.
“We wanted to understand how interactions inside matter affect a superradiant phase transition at thermal equilibrium,” said Motoaki Bamba, an associate professor at Yokohama National University’s Faculty of Engineering. He noted that many simple models omit interactions found in real materials.
The researchers said the exactly solvable model provides a reference point for analyzing more complex light-matter systems. Unlike several recent studies of cavity-coupled one-dimensional systems that focused on absolute-zero behavior, this work examines their properties at finite temperatures.
The team plans to incorporate energy loss and investigate more realistic platforms, including superconducting-qubit arrays and one-dimensional magnets coupled to sub-terahertz cavities. The work is intended to help clarify and control equilibrium phases involving light and matter.
The study, “Exactly solvable phase transition in a cavity-coupled one-dimensional Ising chain,” was authored by Shuntaro Otake and colleagues and published in Physical Review Research in 2026. Its DOI is 10.1103/fxml-nv46.
Sources: Phys.org.