Experiments with Linear, Nonlinear, and Topological Excitations in a Superfluid Gas

R. Y. Chiao, Jack Boyce

The Bogoliubov dispersion relation for the elementary excitations of the weakly-interacting Bose gas is shown to hold for the case of the weakly-interacting photon gas (the ``photon fluid'') in a nonlinear Fabry-Perot cavity. This relation, which is also derived by means of a linearized fluctuation analysis in classical nonlinear optics, implies the possibility of a new superfluid state of light. The theory underlying an experiment in progress to measure this dispersion relation is described, and another experiment to test the prediction of the superfluidity of this state of light is proposed.

Yuki Kawaguchi, Masahito Ueda

Jan Max Walter Krüger

R. Y. Chiao, Jack Boyce

The Bogoliubov dispersion relation for the elementary excitations of the weakly interacting Bose gas is shown to hold for the case of the weakly interacting photon gas (the ``photon fluid'') in a nonlinear Fabry-Perot cavity. The chemical potential of a photon in the two-dimensional photon fluid does not vanish. The Bogoliubov relation, which is also derived by means of a linearized fluctuation analysis in classical nonlinear optics, implies the possibility of a new, superfluid state of light. The theory underlying an experiment in progress to observe sound waves in the photon fluid is described, and another experiment to measure the critical velocity of this superfluid is proposed.

J. Beugnon

Jian Feng, Weiwei Zhang, Liang-Wei Lin +4 more

Topological superfluid state is different from the normal superfluid one due to the excitation energy gap on the boundary. How to obtain the topological superfluid state by using spin–orbit coupling to control the s-waves paired mass-imbalanced Fermi gas is a recent novel topic. In this paper, we study the topological superfluid phase diagram of two-dimensional mass-imbalanced Fermi gas with Rashba spin–orbit coupling at zero temperature. We find that due to the competition among mass imbalance, pairing interaction and spin–orbit coupling, there is a double-well structure in the thermodynamic potential, which affects the properties of the ground state of the system. We comprehensively give the phase diagrams of the system on the plane of spin–orbit coupling and chemical potential, and the phase diagrams on the plane of the reduced mass ratio and two-body binding energy. This study not only points out the stable region of topological superfluid state of mass-imbalanced Fermi gas, but also provides a detailed theoretical basis for better observation of topological superfluid state in experiments.