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arXiv:2012.10098 · Physical Review A

Superradiant phase transition with cavity-assisted dynamical spin-orbit coupling

Ying Lei, Shaoliang Zhang

Published May 21, 2021• 2 citations
arXivHTMLPDF

Abstract

The superradiant phase transition represents an important quantum phenomenon that shows collective excitations based on the coupling between atoms and cavity modes. Spin-orbit coupling is another quantum effect which is induced by the interaction of the atomic internal degrees of freedom and center-of-mass momentum. In this work we consider the cavity-assisted dynamical spin-orbit coupling which comes from the combination of these two effects. It can generate a series of interesting quantum phenomena such as the flat spectrum and the discontinuity of the excitation energy spectrum around the critical point of the quantum phase transition. We further discuss the influence of atom decay and nonlinear coupling on the phase diagram. The atom decay suppresses the discontinuity of the phase diagram and the nonlinear coupling can break the symmetric properties of the phase transition. Our work provides a theoretical method to research the rich quantum phenomena in this dynamic many-body system.

DOI
10.1103/physreva.103.053318

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In cold atom, the coupling between "spin" (atomic internal hyperfine states) and "orbit" (atomic center-of-mass motion) can be induced by Raman transition, where different hyperfine states are coupled by a pair of Raman lasers. In recent years, this synthetic spin-orbit coupling has received tremendous attention, as it leads to a variety of novel quantum phenomena in precisely controllable cold atom systems. In this thesis, we first present a comprehensive analysis of one-, two- and many- particle physics of harmonically trapped atoms with spin-orbit coupling, followed by the study of "novel spin-orbit coupling" in two different systems: (1) cold atom spinor mixtures and (2) cold atoms in an optical cavity. In the first system, we consider a spinor mixture consisting of two species of cold atoms, where the spin-orbit coupling can be transmitted from one species to the other, and we discuss novel topological properties and the supersolid stripe phase in this mixture. In the second system, we consider the coupling among three parts: the cavity photon field, the atomic internal hyperfine states, and the atomic external center-of-mass motion, and we discuss how this coupling affects familiar quantum optical phenomena, such as Rabi oscillation and Dicke superradiance phase transition. Our novel systems contribute new and practical platforms for the research field of synthetic spin-orbit coupling in cold atoms.
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We consider an atom inside a ring cavity, where a plane-wave cavity field together with an external coherent laser beam induces a two-photon Raman transition between two hyperfine ground states of the atom. This cavity-assisted Raman transition induces effective coupling between atom’s internal degrees of freedom and its center-of-mass motion. In the meantime, atomic dynamics exerts a back-action to cavity photons. We investigate the properties of this system by adopting a mean-field and a full quantum approach, and show that the interplay between the atomic dynamics and the cavity field gives rise to intriguing nonlinear phenomena.