Cavity exciton-polaritons 1,2 (polaritons) are bosonic quasiparticles offering a unique solid-state system for investigating interacting condensates 3-10 . Up to now, disorder-induced localization and short lifetimes 4,6,11 have prevented the establishment of long-range off-diagonal order 12 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 13,14 and localization of condensates in a trap with optically controlled dimensions.Modern semiconductor technology allows the realization of nanostructures where both electronic and photonic states undergo quantum confinement. In particular in semiconductor microcavities, excitons confined in quantum wells and photons confined in a Fabry-Perot resonator can enter the light-matter strong coupling regime. This gives rise to the formation of cavity polaritons, mixed exciton-photon states that obey bosonic statistics 2 . The polariton dispersion presents a sharp energy minimum close to the states with zero in-plane wave vector (k = 0) with an effective mass m * three orders of magnitude smaller than that of the bare quantum well exciton. Recently, polariton Bose-Einstein condensation 3-10 (BEC) and related effects such as vortices 15,16 or superfluid 17-19 behaviour have been reported at unprecedented high temperatures. As a result of their finite lifetime, cavity polaritons are a model system to investigate dynamical BEC (refs 20,21), also referred to as a polariton laser effect, with a technological control of the resonator geometry and the polariton lifetime. In previously reported polariton laser systems, the cavity lifetime and the photonic disorder prevented the build-up of extended condensates needed for the realization of polariton circuits 22,23 . The measured coherence length ranged at best from 10 to 20 µm (refs 4,6,11,24), a few times the polariton thermal de Broglie wavelength.Here, we report on the spontaneous formation of extended polariton condensates with a spatial coherence extending over 50 times the thermal de Broglie wavelength. These condensates, made of a quantum degenerated light-matter state, are strongly out of equilibrium, thus deeply differing from atomic BEC. Spatial control of such extended condensates is demonstrated, opening the way to a new range of physic...

Polariton lasing is demonstrated on the zero dimensional states of single GaAs/GaAlAs micropillar cavities. Under non resonant excitation, the measured polariton ground state occupancy is found to be as large as 10 4 . Changing the spatial excitation conditions, competition between several polariton lasing modes is observed, ruling out Bose-Einstein condensation. When the polariton state occupancy increases, the emission blueshift is the signature of self-interaction within the halflight half-matter polariton lasing mode.PACS numbers: 78.55. Et, 71.36.+c, 78.45.+h Boson statistics can lead to massive occupation of a single quantum state and trigger final state stimulation. This stimulation is responsible for the bright coherent emission of light in a laser. Another fascinating property of massive bosons in thermal equilibrium is their ability to accumulate in the lowest energy state under a given critical temperature. First predicted in 1925,[1] the experimental observation of Bose Einstein condensation was achieved in the mid 1990s for ultra-cold atoms. [2,3] Demonstrating such bosonic effects with matter waves in a solid state system is very interesting both from fundamental point of view but also for applications since it could provide a new source of coherent light. Cavity polaritons are an example of quasi-particles behaving as bosons at low density. [4,5] They are the exciton-photon mixed quasi-particles arising from the strong coupling regime between quantum well (QW) excitons and a resonant optical cavity mode. Because of their very small effective mass (10 −8 times that of the hydrogen atom) cavity polaritons are expected to condensate at unusually high temperatures (up to room temperature in wide band gap microcavities).[6] These last years, massive occupation of a polariton state has been observed in semiconductor two-dimensional (2D) cavities and attributed to Bose Einstein condensation [7,8] or to polariton lasing. [9] More recently, polariton condensation has been claimed in a localized energy trap [10] where the trap dimensions are sufficiently large for the system to present a 2D continuum of polariton states. In these experiments, the clear distinction of a thermodynamic phase transition (Bose Einstein condensation) from a kinetic stimulated scattering (polariton lasing) is still debated.In this letter, we demonstrate polariton lasing in micrometric sized GaAs/GaAlAs micropillar cavities. In such zero-dimensional (0D) cavities, polariton states are confined in all directions and present a well defined discretized energy spectrum. [11,12] The absence of translation invariance lifts the wave-vector conservation selection-rules in polariton scatterings. In GaAs 2D microcavities, these selection rules are responsible for inefficient polariton-phonon or polariton-polariton scattering, preventing the build-up of a large occupancy in the lower energy states. [13,14,15,16] In this work, we show that polariton scattering is very efficient in micropillar cavities. Under non resonant excitation, a thres...

The greatly enhanced fields near metal nanoparticles have demonstrated remarkable optical properties and are promising for applications from solar energy to biosensing. However, direct experimental study of these light-matter interactions at the nanoscale has remained difficult due to the limitations of optical microscopy. Here, we use single-molecule fluorescence imaging to probe how a plasmonic nanoantenna modifies the fluorescence emission from a dipole emitter. We show that the apparent fluorophore emission position is strongly shifted upon coupling to an antenna and that the emission of dyes located up to 90 nm away is affected by this coupling. To predict this long-ranged effect, we present a framework based on a distance-dependent partial coupling of the dye emission to the antenna. Our direct interpretation of these light-matter interactions will enable more predictably optimized, designed, and controlled plasmonic devices and will permit reliable plasmon-enhanced single-molecule nanoscopy.

We report on polariton condensation in photonic molecules formed by two coupled micropillars. We show that the condensation process is strongly affected by the interaction with the cloud of uncondensed excitons. Depending on the spatial position of these excitons within the molecule, condensation can be triggered on both binding and anti-binding polariton states of the molecule, on a metastable state or a total transfer of the condensate into one of the micropillars can be obtained. Our results highlight the crucial role played by relaxation kinetics in the condensation process.PACS numbers: 71.36.+c, 67.85.Hj, 78.67.Pt, 78.55.Cr Most of the experimental studies in atomic Bose condensates have explored conditions of thermodynamic equilibrium since typical condensate lifetimes are much longer than interaction times. Recent theoretical proposals have shown that out of equilibrium bosonic systems present qualitatively new behaviors [1]. One proposed way to reach this regime is the use of photonic systems with effective photon-photon interactions and dissipation provided by inherent optical losses [2]. Localized to delocalized phase transitions [3,4], highly entangled states [5], or fermionisation effects in a ring of coupled sites [6] are predicted in such systems.Microcavity polaritons are a model system for the investigation of the physics of driven-dissipative boson condensates [7][8][9][10][11][12][13]. They are the quasi-particules arising from the strong coupling between excitons confined in quantum wells and the optical mode of a microcavity. Because of their light-matter nature, polaritons present peculiar properties: they interact efficiently with their environment through their excitonic part [14,15] while their photonic part enables efficient coupling with the free space optical modes. Polariton condensates can be generated in zero dimensional micropillars [11] or in arrays of pillars with fully controlled coupling [16,17]. In this configuration, the non-equilibrium nature of polariton condensates should allow the realization of metastable collective states, such as the self-trapped states in a bosonic Josephson junction [18][19][20].In the present paper we investigate polariton condensation in photonic molecules obtained by coupling two micropillars. We demonstrate that polariton interactions strongly affect the way condensation occurs in such coupled system, not only modifying the wavefunction of the polariton condensate, but also the relaxation dynamics. This effect, specific to an out-of-equilibrium bosonic system, is illustrated by considering different positions of the non resonant excitation within the molecule. When the excitation spot is placed at the center of the molecule, polariton condensation is observed on both binding and anti-binding states. Interactions induce strong changes in the condensate wavefunction, the most important one being the change in its spatial anisotropy.When the excitation spot is positioned on one of the two coupled micropillars, condensation occurs in a very diffe...