Nonlinear Atom-Photon Interaction Induced Population Inversion and Inverted Quantum Phase Transition of Bose-Einstein Condensate in an Optical Cavity

TL;DR

This paper investigates how nonlinear atom-photon interactions in a Bose-Einstein condensate within an optical cavity lead to novel phenomena like population inversion and inverted quantum phase transitions, expanding understanding of quantum state control.

Contribution

It introduces the concept of nonlinear atom-photon interactions causing inverted quantum phase transitions and bistability in Bose-Einstein condensates in optical cavities.

Findings

Observation of population inversion in the system.

Identification of an inverted quantum phase transition.

Analytical derivation of bistable macroscopic states.

Abstract

In this paper we explore the rich structure of macroscopic many-particle quantum states for Bose- Einstein condensate in an optical cavity with the tunable nonlinear atom-photon interaction [Nature (London) 464, 1301 (2010)]. Population inversion, bistable normal phases and the coexistence of normal{superradiant phases are revealed by adjusting of the experimentally realizable interaction strength and pump-laser frequency. For the negative (effective) cavity-frequency we observe remark- ably an inverted quantum phase transition (QPT) from the superradiant to normal phases with the increase of atom-field coupling, which is just opposite to the QPT in the normal Dicke model. The bistable macroscopic states are derived analytically in terms of the spin-coherent-state variational method by taking into account of both normal and inverted pseudospin states.