Microcavity polaritons are composite half-light half-matter quasi-particles, which have recently been demonstrated to exhibit rich physical properties, such as non-equilibrium Bose-Einstein condensation, parametric scattering and superfluidity. At the same time, polaritons have some important advantages over photons for information processing applications, since their excitonic component leads to weaker diffraction and stronger inter-particle interactions, implying, respectively, tighter localization and lower powers for nonlinear functionality. Here we present the first experimental observations of bright polariton solitons in a strongly coupled semiconductor microcavity. The polariton solitons are shown to be non-diffracting high density wavepackets, that are strongly localised in real space with a corresponding broad spectrum in momentum space. Unlike solitons known in other matter-wave systems such as Bose condensed ultracold atomic gases, they are non-equilibrium and rely on a balance between losses and external pumping. Microcavity polariton solitons are excited on picosecond timescales, and thus have significant benefits for ultrafast switching and transfer of information over their light only counterparts, semiconductor cavity lasers (VCSELs), which have only nanosecond response time
We demonstrate that the tunable potential introduced by a surface acoustic wave on a homogeneous polariton condensate leads to fragmentation of the condensate into an array of wires which move with the acoustic velocity. Reduction of the spatial coherence of the condensate emission along the surface acoustic wave direction is attributed to the suppression of coupling between the spatially modulated condensates. Interparticle interactions observed at high polariton densities screen the acoustic potential, partially reversing its effect on spatial coherence.
We report on the two-dimensional gap-soliton nature of exciton-polariton macroscopic coherent phases (PMCP) in a square lattice with a tunable amplitude. The resonantly excited PMCP forms close to the negative mass M point of the lattice band structure with energy within the lattice band gap and its wave function localized within a few lattice periods. The PMCPs are well described as gap solitons resulting from the interplay between repulsive polariton-polariton interactions and effective attractive forces due to the negative mass. The solitonic nature accounts for the reduction of the PMCP coherence length and optical excitation threshold with increasing lattice amplitude. DOI: 10.1103/PhysRevLett.111.146401 PACS numbers: 71.36.+c, 42.65.Yj, 63.20.kk, 73.21.Cd The periodic spatial modulation of a medium creates an artificial band structure with energy gaps and anomalous (i.e., negative) dispersion. In the presence of nonlinearity, spatially self-localized states may appear within the energy gaps as the result of the interplay between the anomalous dispersion and interparticle interactions. This takes place when the kinetic energy contribution [E K ¼ À 2 @ 2 =ð2m b 2 Þ] due to localization of particles with a negative mass Àm b within a radius compensates the repulsive interparticle interaction energy E I . These states, known as gap solitons (GSs), are metastable solutions of the Gross-Pitaevskii equation [1]. GSs have been explored in optical fibers [2], nonlinear photonic crystals [3-6], atomic Bose Einstein condensates (BECs) in optical lattices [7,8], and, very recently, also in the hybrid lightmatter polariton system [9]. Polaritons result from the strong coupling of photons and quantum well (QW) excitons in a semiconductor microcavity (MC). Being bosonic light-matter quasiparticles, they advantageously combine features from both species. Namely, the small mass arising from the photonic component allows them to form polariton macroscopic coherent phases (PMCPs) at low densities and high temperatures, while the interexcitonic interactions provide a nonlinearity several orders of magnitude stronger than in purely photonic systems [10]. While GSs in one-dimensional (1D) potentials have been extensively studied [2,3,5,[7][8][9], GSs in 2D lattices have so far only been reported for purely photonic systems [4,6]. GSs in 2D potentials are qualitatively different from their 1D counterparts, for example, opening the way to the realization of novel topological phases [6,11].In this Letter, we demonstrate the formation and manipulation of GSs of PMCPs in a 2D tunable lattice. The studies were carried out in PMCPs resonantly excited in a tunable square lattice created by surface acoustic waves (SAWs). While PMCPs in a homogeneous MC normally appear at the lowest energy state with zero in-plane momentum, PMCPs in a shallow (i.e., low amplitude) lattice have a GS character and are excited via the accumulation of particles at critical points of negative mass and energy above the ground state [12]. The PMCP forms clo...
We demonstrate the creation of vortices in a macroscopically occupied polariton state formed in a semiconductor microcavity. A weak external laser beam carrying orbital angular momentum (OAM) is used to imprint a vortex on the condensate arising from the polariton optical parametric oscillator (OPO). The vortex core radius is found to decrease with increasing pump power, and is determined by polariton-polariton interactions. As a result of OAM conservation in the parametric scattering process, the excitation consists of a vortex in the signal and a corresponding antivortex in the idler of the OPO. The experimental results are in good agreement with a theoretical model of a vortex in the polariton OPO.
The design and the performance of a 4.7-THz local oscillator (LO) for the GREAT (German REceiver for Astronomy at Terahertz frequencies) heterodyne spectrometer on SOFIA, the Stratospheric Observatory for Infrared Astronomy, are presented. The LO is based on a quantum-cascade laser, which is mounted in a compact mechanical cryocooler. The LO provides up to 150 W output power into a nearly Gaussian shaped beam. It covers the frequency range from approximately 2 to 4 GHz around the fine structure line of neutral atomic oxygen, OI, at 4.7448 THz. The LO has been successfully operated on SOFIA during six observation flights in May 2014 and January 2015. Index Terms-Heterodyne spectroscopy, local oscillator (LO), quantum-cascade laser (QCL), SOFIA, terahertz (THz). 2156-342X
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