Dicke model of open-shell atoms with tensor polarizability

Abstract

We study the extended Dicke model obtained from the scalar--vector--tensor polarizability of open-shell atoms coupled to a shared cavity mode. For a single electric-dipole channel, rotational symmetry fixes the tensor to vector ratio; we use $^{168}\mathrm{Er}$ with $J=6$ as a product-state example. A circular pump produces a chiral Raman vertex whose tensor-dependent matrix elements select the occupied Zeeman sector. The resulting first-order transition occurs before the empty-cavity branch loses local stability, and the ordered state is read out through $\langle\hat J_z\rangle$. A linear pump instead produces an empty-cavity $\pm x$ cat and a continuous transition into an even-$m$ cat-like state with order parameter $\langle\hat J_z^2\rangle$. With cavity loss alone, the circular trajectory emits a photon burst and approaches a Raman-dark Zeeman pole rather than a finite-field condensate. In the linear geometry, cavity-bright modes are damped toward the cat-like branch while a dark spin mode remains undamped. These are phenomena of that model; the vector-only controls show that they depend on the channel-fixed tensor coupling.