Coherent Oscillations in an Exciton-Polariton Josephson Junction

We report on the observation of spontaneous coherent oscillations in a microcavity polariton bosonic Josephson junction. The condensation of exciton polaritons takes place under incoherent excitation in a disordered environment, where double potential wells tend to appear in the disordered landscape. Coherent oscillations set on at an excitation power well above the condensation threshold. The time resolved population and phase dynamics reveal the analogy with the AC Josephson effect. We have introduced a theoretical two-mode model to describe the observed effects, which allows us to explain how the different realizations of the pulsed experiment have a similar phase relation

Annealing induced ordering of SrTiO3 thin films deposited by laser ablation over Si substrates

Strontium titanate thin films have been prepared at different oxygen pressures and with different post deposition annealing treatments. The films were deposited by laser ablation at room temperature on Si(001) substrates with a silica buffer layer. The as-deposited films are amorphous with smooth and uniform surface. As the annealing temperature increase they become more crystalline, presenting a cubic SrTiO3 phase. The infrared characterization show that the silica layer also grows due to the annealing. The characteristics of this SrTiO3 crystalline depend on the oxygen partial pressure. At low oxygen pressures the annealed films are polycrystalline. As the oxygen pressure increase the films become more textured so that at longer enough annealing times the films become (200) oriented. The results are discussed in terms of atomic diffusion in the films.(undefined

2s exciton-polariton revealed in an external magnetic field

We demonstrate the existence of the excited state of an exciton-polariton in a semiconductor microcavity. The strong coupling of the quantum well heavy-hole exciton in an excited 2s state to the cavity photon is observed in non-zero magnetic field due to surprisingly fast increase of Rabi energy of the 2s exciton-polariton in magnetic field. This effect is explained by a strong modification of the wave-function of the relative electron-hole motion for the 2s exciton state.Comment: 5 pages, 5 figure

Dynamics of long-range order in an exciton-polariton condensate

We report on time resolved measurements of the first order spatial coherence in an exciton polariton Bose-Einstein condensate. Long range spatial coherence is found to set in right at the onset of stimulated scattering, on a picosecond time scale. The coherence reaches its maximum value after the population and decays slower, staying up to a few hundreds of picoseconds. This behavior can be qualitatively reproduced, using a stochastic classical field model describing interaction between the polariton condensate and the exciton reservoir within a disordered potential.Comment: 7 pages, 4 figure

Data analysis of gravitational-wave signals from spinning neutron stars. V. A narrow-band all-sky search

We present theory and algorithms to perform an all-sky coherent search for periodic signals of gravitational waves in narrow-band data of a detector. Our search is based on a statistic, commonly called the $\mathcal{F}$-statistic, derived from the maximum-likelihood principle in Paper I of this series. We briefly review the response of a ground-based detector to the gravitational-wave signal from a rotating neuron star and the derivation of the $\mathcal{F}$-statistic. We present several algorithms to calculate efficiently this statistic. In particular our algorithms are such that one can take advantage of the speed of fast Fourier transform (FFT) in calculation of the $\mathcal{F}$-statistic. We construct a grid in the parameter space such that the nodes of the grid coincide with the Fourier frequencies. We present interpolation methods that approximately convert the two integrals in the $\mathcal{F}$-statistic into Fourier transforms so that the FFT algorithm can be applied in their evaluation. We have implemented our methods and algorithms into computer codes and we present results of the Monte Carlo simulations performed to test these codes.Comment: REVTeX, 20 pages, 8 figure

Polariton Condensation in a One-Dimensional Disordered Potential

We study the coherence and density modulation of a non-equilibrium exciton-polariton condensate in a one-dimensional valley with disorder. By means of interferometric measurements we evidence a modulation of the first-order coherence function and we relate it to a disorder-induced modulation of the condensate density, that increases as the pump power is increased. The non-monotonous spatial coherence function is found to be the result of the strong non-equilibrium character of the one-dimensional system, in the presence of disorder

Probing the Dynamics of Spontaneous Quantum Vortices in Polariton Superfluids

The experimental investigation of spontaneously created vortices is of utmost importance for the understanding of quantum phase transitions towards a superfluid phase, especially for two dimensional systems that are expected to be governed by the Berezinski-Kosterlitz-Thouless physics. By means of time resolved near-field interferometry we track the path of such vortices, created at random locations in an exciton-polariton condensate under pulsed non-resonant excitation, to their final pinning positions imposed by the stationary disorder. We formulate a theoretical model that successfully reproduces the experimental observations

Optical manipulation of the wave function of quasiparticles in a solid

Polaritons in semiconductor microcavities are hybrid quasiparticles consisting of a superposition of photons and excitons. Due to the photon component, polaritons are characterized by a quantum coherence length in the several micron range. Owing to their exciton content, they display sizeable interactions, both mutual and with other electronic degrees of freedom. These unique features have produced striking matter wave phenomena, such as Bose-Einstein condensation, or parametric processes able to generate quantum entangled polariton states. Recently, several paradigms for spatial confinement of polaritons in semiconductor devices have been established. This opens the way to quantum devices in which polaritons can be used as a vector of quantum information. An essential element of each quantum device is the quantum state control. Here we demonstrate control of the wave function of confined polaritons, by means of tailored resonant optical excitation. By tuning the energy and momentum of the laser, we achieve precise control of the momentum pattern of the polariton wave function. A theoretical model supports unambiguously our observations