Synchronized and desynchronized phases of coupled non-equilibrium exciton-polariton condensates

We theoretically analyze the synchronized and desynchronized phases of coupled non-equilibrium polariton condensates within mean field theory. An analytical condition for the existence of a synchronized phase is derived for two coupled wells. The case of many wells in a 2D disordered geometry is studied numerically. The relation to recent experiments on polariton condensation in CdTe microcavities is discussed.Comment: 5 pages, 3 figure

Probing the excitation spectrum of nonresonantly pumped polariton condensates

We propose a four wave mixing experiment to probe the elementary excitation spectrum of a non-equilibrium Bose-Einstein condensate of exciton-polaritons under non-resonant pumping. Analytical calculations based on mean-field theory show that this method is able to reveal the characteristic negative energy feature of the Bogoliubov dispersion. Numerical simulations including the finite spatial profile of the excitation laser spot and a weak disorder confirm the practical utility of the method for realistic condensates.Comment: 7 pages, 5 figure

Superfluid to Bose-glass transition in a 1D weakly interacting Bose gas

We study the one-dimensional Bose gas in spatially correlated disorder at zero temperature, using an extended density-phase Bogoliubov method. We analyze in particular the decay of the one-body density matrix and the behaviour of the Bogoliubov excitations across the phase boundary. We observe that the transition to the Bose glass phase is marked by a power-law divergence of the density of states at low energy. A measure of the localization length displays a power-law energy dependence in both regions, with the exponent equal to -1 at the boundary. We draw the phase diagram of the superfluid-insulator transition in the limit of small interaction strength.Comment: 4 pages, 4 figure

Excitations in a non-equilibrium Bose-Einstein condensate of exciton-polaritons

We have developed a mean-field model to describe the dynamics of a non-equilibrium Bose-Einstein condensate of exciton-polaritons in a semiconductor microcavity. The spectrum of elementary excitations around the stationary state is analytically studied in different geometries. A diffusive behaviour of the Goldstone mode is found in the spatially homogeneous case and new features are predicted for the Josephson effect in a two-well geometry.Comment: 5 pages, 2 figure

Mean-field phase diagram of the 1-D Bose gas in a disorder potential

We study the quantum phase transition of the 1D weakly interacting Bose gas in the presence of disorder. We characterize the phase transition as a function of disorder and interaction strengths, by inspecting the long-range behavior of the one-body density matrix as well as the drop in the superfluid fraction. We focus on the properties of the low-energy Bogoliubov excitations that drive the phase transition, and find that the transition to the insulator state is marked by a diverging density of states and a localization length that diverges as a power-law with power 1. We draw the phase diagram and we observe that the boundary between the superfluid and the Bose glass phase is characterized by two different algebraic relations. These can be explained analytically by considering the limiting cases of zero and infinite disorder correlation length.Comment: 10 pages, 10 figure

Spatial and spectral shape of inhomogeneous non-equilibrium exciton-polariton condensates

We develop a mean-field theory of the spatial profile and the spectral properties of polariton condensates in nonresonantly pumped semiconductor microcavities in the strong coupling regime. Predictions are obtained for both the continuous-wave and the pulsed excitation regimes and the specific signatures of the non-equilibrium character of the condensation process are pointed out. A striking sensitivity of the condensate shape on the optical pump spot size is demonstrated by analytical and numerical calculations, in good quantitative agreement with recent experimental observations.Comment: 5 pages, 3 figure

Energy-weighted density matrix embedding of open correlated chemical fragments

We present a multi-scale approach to efficiently embed an ab initio correlated chemical fragment described by its energy-weighted density matrices, and entangled with a wider mean-field many-electron system. This approach, first presented in Phys. Rev. B, 98, 235132 (2018), is here extended to account for realistic long-range interactions and broken symmetry states. The scheme allows for a systematically improvable description in the range of correlated fluctuations out of the fragment into the system, via a self-consistent optimization of a coupled auxiliary mean-field system. It is discussed that the method has rigorous limits equivalent to existing quantum embedding approaches of both dynamical mean-field theory, as well as density matrix embedding theory, to which this method is compared, and the importance of these correlated fluctuations is demonstrated. We derive a self-consistent local energy functional within the scheme, and demonstrate the approach for Hydrogen rings, where quantitative accuracy is achieved despite only a single atom being explicitly treated.Comment: 14 pages, 8 figure

Trajectories and regimes in research versus knowledge evaluations:Contributions to an evolutionary theory of citation

Citation analysis can provide us with models of the evolutionary dynamics in scholarly and scientific communication. We propose to distinguish between institutional research evaluation (usually, ex post) and knowledge evaluation ex ante, in relation to directionality in citation analysis. We discuss the theoretical literature on communication systems which dis-tinguishes between information and meaning, in which the concept of redundancy plays an important role as measure of the potential of a communication system. This is the basis for a model of knowledge dynamics which differentiates between observable variation and latent selection environments. We use indicators at the journal level and analyze the citation environments of journals in both the cited and citing directions. Among journals, the citing direction can be analyzed by co-citation and indicates the integration of knowledge from different fields. The cited direction can analo-gously be analyzed by bibliographic coupling and represents the extent to which the cited journal has become relevant for different disciplines, hence indicates knowledge diffusion. We apply this analysis on three different case studies of journal-journal relations: a small scale study of the journal Public Understanding of Science, a random sample of 100 journals, and a large-scale analysis of the set of JCR 2016 journals. Combined, the results seem to confirm the hypothe-sis that interdisciplinarity cannot be captured by one-dimensional citation analysis. Both citing and cited directions are relevant for knowledge and research evaluations, respectively. We raise the question whether indicators of interdisci-plinarity can be developed by combining both directions in citation analysis, indicate further research, and discuss the normative implications of our preliminary results

The stability of nonequilibrium polariton superflow in the presence of a cylindrical defect

We make a theoretical study of the stability of nonequilibrium polariton superflows that interact with a cylindrical defect. The nonresonantly pumped polariton condensate is modelled with a generalized complex Ginzburg-Landau equation. At low pump intensities the dissipation is found stabilize the superflow. At large pump intensities, we find an instability that sets a lower critical speed for superfluidity. For even larger pump power, the lower and upper critical speed meet and stable superflows are no longer possible.Comment: 5 pages, 5 figure