Topological Unwinding in an Exciton-Polariton Condensate Array

The phase distribution in a Bose-Einstein condensate can realize various topological states which can be classified according to distinct winding numbers. While states with different winding numbers are topologically protected in the linear Schr\"odinger equation, when nonlinearities are introduced, violations of the topological protection can occur, leading to unwinding. Exciton-polariton condensates constitute a weakly nonlinear open dissipative system that is well suited to studying such physics. Here we show that exciton-polariton condensates display a spontaneous phase unwinding from a $\pi$- to zero-state. While such an effect was previously observed in a one-dimensional polariton-condensate array and explained as occurring due to single-particle mode competition, we offer a new explanation in terms of collective phase unwinding of metastable states. We clarify that the collective transition is caused by the combined effect of nonlinearity and topological defects in the condensates. Reanalyzing the experimental data, we find an evidence of the collective phase unwinding.Comment: 8+4 pages, 4+1 figure

Multicritical dissipative phase transitions in the anisotropic open quantum Rabi model

We investigate the nonequilibrium steady state of the anisotropic open quantum Rabi model, which exhibits first-order and second-order dissipative phase transitions upon varying the degree of anisotropy between the coupling strengths of rotating and counterrotating terms. Using both semiclassical and quantum approaches, we find a rich phase diagram resulting from the interplay between the anisotropy and the dissipation. First, there exists a bistable phase where both the normal and superradiant phases are stable. Second, there are multicritical points where the phase boundaries for the first- and second-order phase transitions meet. We show that a new set of critical exponents governs the scaling of the multicritical points. Finally, we discuss the feasibility of observing the multicritical transitions and bistability using a pair of trapped ions where the anisotropy can be tuned by the controlling the intensity of the Raman transitions. Our study enlarges the scope of critical phenomena that may occur in finite-component quantum systems, which could be useful for the applications in the critical quantum sensing.Comment: 11 pages, 5 figure

Long-Term Infection and Pathogenesis in a Novel Mouse Model of Human Respiratory Syncytial Virus

Intensive efforts have been made to develop models of hRSV infection or disease using various animals. However, the limitations such as semi-permissiveness and short duration of infection have impeded their applications in both the pathogenesis of hRSV and therapeutics development. Here, we present a mouse model based on a Rag2 gene knockout using CRISPR/Cas9 technology. Rag2−/− mice sustained high viral loads upon intranasal inoculation with hRSV. The average peak titer rapidly reached 1 × 109.8 copies/g and 1c106 TCID50 in nasal cavity, as well as 1 × 108 copies/g and 1 × 105 TCID50 in the lungs up to 5 weeks. Mild interstitial pneumonia, severe bronchopneumonia, elevated cytokines and NK cells were seen in Rag2−/− mice. A humanized monoclonal antibody showed strong antiviral activity in this animal model, implying that Rag2−/− mice that support long-term stable infection are a useful tool for studying the transmission and pathogenesis of human RSV, as well as evaluating therapeutics