Chongqing University team discovers similar quantum magnetism in the superradiant phase under artificial magnetic field modulation
On October 25, 2022, Professor Yuyu Zhang and her researcher Guojing Yang from the School of Physics, Chongqing University, in collaboration with Professor Han Pu's team from Rice University, published a research paper titled "Understanding the Quantum Rabi The research paper entitled "Understanding the Quantum Rabi Ring Using Analogies to Quantum Magnetism" was published in Physical Review Letters.
In recent years there has been a strong interest in the Dzyaloshinskii-Moriya (DM) interaction of spins in magnetic materials, since this magnetic interaction always causes adjacent spins to tend to align perpendicular to each other. the competition between the DM interaction and the ferromagnetic interaction forms the left-handed and right-handed rotating helical magnetic structures of the spin wave vector, called chiral magnets, and the appearance of magnetic sigmoids ( skyrmion) and other interesting phenomena. Unlike real magnetic materials, equivalent pseudomagnetic systems are more likely to achieve different magnetic interactions and modulation of the strength of the interactions. Light-matter interaction systems are highly artificially manipulable and can simulate magnetic interactions and phenomena that are difficult to achieve in real magnetic systems.
In the work, the team discovered that the light-atom interaction system-quantum Rabi ring can be equated to the quantum magnetic system, and the equivalent spin-DM interaction and XY spin-exchange interaction appear, and the interaction strength is modulated by the artificial magnetic field, and the same quantum phase diagram is obtained for both systems, and the time-reversal symmetry and chiral symmetry breaking of the system are observed. The three superradiant phases in the quantum Rabi ring model in which the photons are excited are described by the competition of the spin-different magnetic interactions, which are equivalent to the ferromagnetic, antiferromagnetic and chiral magnetic phases of the spin-magnetic system; the normal phase in which the photons are not excited is analogous to the paramagnetic phase. In the chiral magnetic phase, where the DM action plays a dominant role, the x and y components of the pseudospin at different lattice points are observed to form a magnetic sigmoid-like structure (as in Figure 1b), which is associated with the complex number order parameter of the chiral superradiant phase.
Eventually, it is found that the critical indices of the excitation energies of the chiral quantum phases are different for odd and even quantum Rabi ring systems, and the chiral magnetic phase belongs to a different phase transition universal class than the ferromagnetic, antiferromagnetic phase.
Figure 1 (a) Quantum phase diagram of the magnetic model with N=4: ferromagnetic phase (FP), antiferromagnetic phase (AFP), chiral magnetic phase (CP), and paramagnetic phase (pp); (b) spin structure in the plane of 4 lattice points in the chiral magnetic phase, similar to the magnetic sigmoid.
This work not only pioneers the study of the association of the chiral superradiant phase with the chiral magnetic nature of spin magnetic systems in quantum optical models, but also can be applied to the simulation of novel quantum phenomena in complex magnetic systems in the future. This research is supported by the National Natural Science Foundation of China, the Natural Science Foundation of Chongqing, and the Fundamental Research Funds of Central Universities - Basic Frontier Crossover Project.
Links to related paper：
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.183602
