Photon Condensation and Enhanced Magnetism in Cavity QED

TL;DR

This paper explores how coupling magnetic molecules to microwave cavities induces superradiant phase transitions, modifies magnetic properties, and enables quantum control of magnetism, with experimental and theoretical insights into cavity QED effects.

Contribution

It demonstrates the equilibrium superradiant phase transition in magnetic molecules coupled to microwave cavities and shows how cavity QED can control magnetic phases and properties.

Findings

Observation of superradiant phase transition in magnetic molecules

Modification of magnetic phase diagram via cavity coupling

Transmission experiments resolving the phase transition

Abstract

A system of magnetic molecules coupled to microwave cavities ($LC$ resonators) undergoes the equilibrium superradiant phase transition. The transition is experimentally observable. The effect of the coupling is first illustrated by the vacuum-induced ferromagnetic order in a quantum Ising model and then by the modification of the magnetic phase diagram of ${\rm Fe_8}$ dipolar crystals, exemplifying the cooperation between intrinsic and photon-induced spin-spin interactions. Finally, a transmission experiment is shown to resolve the transition, measuring the quantum electrodynamical control of magnetism.