The superradiant phase transition (SRPT) in the Dicke model, originally predicted in 1973 and studied for more than 50 years, leads to a striking equilibrium phenomenon: strong quantum squeezing at the critical point [1]. Unlike nonequilibrium squeezing, thermal-equilibrium quantum squeezing is robust against loss and decoherence, as it emerges in the most stable state of the system. While the original photonic SRPT remains unobserved, its magnonic realization has been confirmed in ErFeO3 [2].
In this talk, we present recent theoretical results on the observation of thermal-equilibrium quantum squeezing. We also propose a scheme to generate non-Gaussian states (particularly, Schrödinger-cat states) from the thermal-equilibrium quantum squeezed states. Both results are formulated within the Dicke model and discussed with a particular focus on ErFeO3.

References
[1] K. Hayashida, et al., Sci. Rep. 13, 2526 (2023).
[2] D. Kim, et al., Sci. Adv. 11, eadt1691 (2025); M. Bamba, et al., Commun. Phys. 5, 3 (2022); X. Li, et al., Science 361, 794 (2018).