Zero dimensional exciton-polaritons

We present a novel semiconductor structure in which 0D polaritons coexist with 2D microcavity polaritons. Spatial trapping of the 2D microcavity polaritons results from the confinement of their photonic part in a potential well, consisting of an adjustable thickness variation of the spacer layer. This original technique allows to create polaritonic boxes of any size and shape. Strong coupling regime is evidenced by the typical energy level anticrossing, in real space and in momentum space, and supported by a theoretical model

Engineering the spatial confinement of exciton-polaritons in semiconductors

We demonstrate the spatial confinement of electronic excitations in a solid state system, within novel artificial structures that can be designed having arbitrary dimensionality and shape. The excitations under study are exciton-polaritons in a planar semiconductor microcavity. They are confined within a micron-sized region through lateral trapping of their photon component. Striking signatures of confined states of lower and upper polaritons are found in angle-resolved light emission spectra, where a discrete energy spectrum and broad angular patterns are present. A theoretical model supports unambiguously our observations

Symmetry-breaking Effects for Polariton Condensates in Double-Well Potentials

We study the existence, stability, and dynamics of symmetric and anti-symmetric states of quasi-one-dimensional polariton condensates in double-well potentials, in the presence of nonresonant pumping and nonlinear damping. Some prototypical features of the system, such as the bifurcation of asymmetric solutions, are similar to the Hamiltonian analog of the double-well system considered in the realm of atomic condensates. Nevertheless, there are also some nontrivial differences including, e.g., the unstable nature of both the parent and the daughter branch emerging in the relevant pitchfork bifurcation for slightly larger values of atom numbers. Another interesting feature that does not appear in the atomic condensate case is that the bifurcation for attractive interactions is slightly sub-critical instead of supercritical. These conclusions of the bifurcation analysis are corroborated by direct numerical simulations examining the dynamics of the system in the unstable regime.MICINN (Spain) project FIS2008- 0484

Exciton relaxation and level repulsion in GaAs/AlxGa1-xAs quantum wires

V groove GaAs/AlGaAs quantum wires are investigated by spatially resolved photoluminescence spectroscopy using a low-temperature scanning near- field optical microscope. The spectra along the wires feature several sharp emission lines, which are understood as the emission from exciton states localized in inhomogeneities of the confining potential. It is expected that these exciton states spatially overlap and that their energies are correlated, which leads to level repulsion. The statistical analysis of the spectra in terms of autocorrelation functions clearly reveals this effect. In order to model photoluminescence rather than absorption spectra, we perform detailed simulations of exciton relaxation and luminescence kinetics in a disordered one-dimensional system, taking into account the realistic structure of the facets at the bottom of the V groove in our disorder model. Combining near- field measurements and numerical simulations we show that disorder prevents the full relaxation of excitons towards the local ground states in the dips of the disordered potential. As a consequence, luminescence from excited states is observed. We identify in the spatial and energy correlation between localized states the origin of the observed level repulsion and discuss the role played by the two facets at the bottom of the V groove in this mechanism. This analysis also highlights the relevance of the broad photoluminescence background observed in this and in analogous experiments. We propose as explanation for the origin of this broad background the strong exciton-acoustic phonon coupling that results in phonon sidebands in the spectrum of each localized state

Spontaneous formation and optical manipulation of extended polariton condensates

Cavity exciton-polaritons1, (polaritons) are bosonic quasi-particles offering a unique solid-state system for investigating interacting condensates. Up to now, disorder-induced localization and short lifetimes have prevented the establishment of long-range off-diagonal order needed for any quantum manipulation of the condensate wavefunction. In this work, using a wire microcavity with polariton lifetimes much longer than in previous samples, we show that polariton condensates can propagate over macroscopic distances outside the excitation area, while preserving their spontaneous spatial coherence. An extended condensate wavefunction builds up with a degree of spatial coherence larger than 50% over distances 50 times the polariton de Broglie wavelength. The expansion of the condensate is shown to be governed by the repulsive potential induced by photogenerated excitons within the excitation area. The control of this local potential offers a new and versatile method to manipulate extended polariton condensates. As an illustration, we demonstrate synchronization of extended condensates by controlled tunnel coupling and localization of condensates in a trap with optically controlled dimension