Uniqueness of the phase transition in many-dipole cavity quantum electrodynamical systems

Adam Stokes, Ahsan Nazir

The possibility of a superradiant phase transition in light-matter systems is the subject of much debate, due to numerous apparently conflicting no-go and counter no-go theorems. Using an arbitrary-gauge approach we show that a unique phase transition does occur in archetypal many-dipole cavity QED systems, and that it manifests unambiguously via a macroscopic gauge-invariant polarization. We find that the gauge choice controls the extent to which this polarization is included as part of the radiative quantum subsystem and thereby determines the degree to which the abnormal phase is classed as superradiant. This resolves the long-standing paradox of no-go and counter no-go theorems for superradiance, which are shown to refer to different definitions of radiation.

J. C. Garrison, R. Y. Chiao

Hideo Mabuchi

Erika Cortese, Luigi Garziano, Simone De Liberato

The Dicke-Ising model describes cavity quantum electrodynamics setups in which dipoles couple not only with the photonic cavity field but also with each other through dipole-dipole interaction. In this work we diagonalize such a model in terms of bosonic polaritonic operators for arbitrarily large values of the light-matter coupling and for values of the dipole-dipole interaction until the onset of the ferromagnetic Ising phase transition. In order to accomplish this task we exploit higher-order terms of the Holstein-Primakoff transformation, developing a general method which allows us to solve the normal phase of the Ising model in terms of bosonic excitations for large values of the dipole-dipole interaction. Our results shed light on the interplay between the dipole-dipole and light-matter coupling strengths and their effect on the virtual excitations which populate the ground state when the interactions become comparable with the bare transition frequency.

Pierre Meystre, Murray Sargent

Yamin Huang, Zhen-Qi Hua, Yong-Qing Yang +1 more

Realizing a strong light-matter interaction via magnetic dipoles is of fundamental importance in physics, and a cavity magnonics system has provided a unique platform to achieve strong and even ultrastrong light-matter interaction. In this work, transparency induced by magnon-photon interactions in cavity quantum electrodynamics (QED) system coupling a yttrium-iron-garnet (YIG,Y3Fe5O12) (YIG) sphere has been investigated. The spectral separation reveals a linear relationship with the coupling strength, which might find applications in magnon dark state and magnon-based quantum information processing.