Chirality of topological gap solitons in bosonic dimer chains

We study gap solitons which appear in the topological gap of 1D bosonic dimer chains within the mean-field approximation. We find that such solitons have a non-trivial texture of the sublattice pseudospin. We reveal their chiral nature by demonstrating the anisotropy of their behavior in presence of a localized energy potential

Character, Crafts, and Physique: American Men and the Meaning of Masculinity in World War I and Its Aftermath

In the immediate aftermath of World War I, many Americans were asking questions about what masculinity meant in the context of military service to the nation. American painter Herbert Andrew Paus’s poster “The United States Army Builds Men. Apply Nearest Recruiting Office,” (1919) published by the Niagara Lithograph Company, shows a golden-colored U.S. soldier with his eyes fixed on a globe, surrounded by three distinct figures labeled, and representing, character, crafts, and physique. These three virtues were necessary qualifications for being a soldier, and innate characteristics of American manhood. By applying these three virtues as models for American masculinity in World War I and its aftermath in America, this paper examines their application to subjects such as shell shock, venereal disease, race and eugenics, and post-war reconstruction. Historians have analyzed these characteristics of masculinity in World War I, but have not articulated it by using these three categories, namely character, crafts, and physique. This paper will look not only at the use of this model of masculinity during the war itself, but will also look at where these ideas came from prior to the war, as well as how these ideas played out in the aftermath of the war. This paper will highlight some of the inconsistencies found among these characteristics, as well as the overall breakdown of the model as a whole through its application in WWI-era America

Observation of quantum depletion in a nonequilibrium exciton-polariton condensate

The property of superfluidity, first discovered in liquid 4He, is closely related to Bose-Einstein condensation (BEC) of interacting bosons. However, even at zero temperature, when one would expect the whole bosonic quantum liquid to become condensed, a fraction of it is excited into higher momentum states via interparticle interactions and quantum fluctuations -- the phenomenon of quantum depletion. Quantum depletion of weakly interacting atomic BECs in thermal equilibrium is well understood theoretically but is difficult to measure. This is even more challenging in driven-dissipative systems such as exciton-polariton condensates(photons coupled to electron-hole pairs in a semiconductor), since their nonequilibrium nature is predicted to suppress quantum depletion. Here, we observe quantum depletion of an optically trapped high-density exciton-polariton condensate by directly detecting the spectral branch of elementary excitations populated by this process. Analysis of the population of this branch in momentum space shows that quantum depletion of an exciton-polariton condensate can closely follow or strongly deviate from the equilibrium Bogoliubov theory, depending on the fraction of matter (exciton) in an exciton-polariton. Our results reveal the effects of exciton-polariton interactions beyond the mean-field description and call for a deeper understanding of the relationship between equilibrium and nonequilibrium BECs.Comment: 18 pages, 5 figures, with supplementary informatio

Bogoliubov excitations of a polariton condensate in dynamical equilibrium with an incoherent reservoir

The classic Bogoliubov theory of weakly interacting Bose gases rests upon the assumption that nearly all the bosons condense into the lowest quantum state at sufficiently low temperatures. Here we develop a generalized version of Bogoliubov theory for the case of a driven-dissipative exciton-polariton condensate with a large incoherent uncondensed component, or excitonic reservoir. We argue that such a reservoir can consist of both excitonic high-momentum polaritons and optically dark superpositions of excitons across different optically active layers, such as multiple quantum wells in a microcavity. In particular, we predict interconversion between the dark and bright (light-coupled) excitonic states that can lead to a dynamical equilibrium between the condensate and reservoir populations. We show that the presence of the reservoir fundamentally modifies both the energy and the amplitudes of the Bogoliubov quasiparticle excitations due to the non-Galilean-invariant nature of polaritons. Our theoretical findings are supported by our experiment, where we directly detect the Bogoliubov excitation branches of an optically trapped polariton condensate in the high-density regime. By analyzing the measured occupations of the excitation branches, we extract the Bogoliubov amplitudes across a range of momenta and show that they agree with our generalized theory.Comment: 16 pages, 7 figure