Quantum droplets and Schr\"{o}dinger's cat states in atomic-molecular Bose-Einstein condensates

Abstract

Explicit realization of quantum droplets, even and odd Schr\"{o}dinger cat states is demonstrated in an atom-molecular Bose-Einstein condensate in the presence of interconversion and Kerr non-linear interactions. The crucial roles of both the $\chi^2$-type nonlinearity and chemical potential in the formation of these macroscopic quantum states are shown, where the atomic condensate is in the cat state, with the corresponding molecular wave packet being a quantum droplet. The physical mechanism for their creation and common origin is established to be the non-linearity-induced self-trapping potentials, governed by photoassociation or Feshbach resonance, with the Kerr-type nonlinearities playing subdominant roles. The coexisting and controllable atom and molecular droplets are shown to realize the atom-molecular squeezed state with profiles ranging from Gaussian to flat-top super-Gaussian form. The Wigner functions are exhibited revealing the cat states' phase space interference and squeezing of droplets.