Dispersion of interacting spinor cavity polaritons out of thermal equilibrium (original) (raw)
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Quantum-fluid dynamics of microcavity polaritons
Nature, 2007
Semiconductor microcavities offer a unique system to investigate the physics of weakly interacting bosons. Their elementary excitations, polaritons--a mixture of excitons and photons--behave, in the low density limit, as bosons that can undergo a phase transition to a regime characterised by long range coherence. Condensates of polaritons have been advocated as candidates for superfluidity; and the formation of vortices as well as elementary excitations with a linear dispersion are actively sought after. In this work, we have created and set in motion a macroscopically degenerate state of polaritons and let it collide with a variety of defects present in the sample. Our experiments show striking manifestations of a coherent light-matter packet that displays features of a superfluid, although one of a highly unusual character as it involves an out-of-equilibrium dissipative system where it travels at ultra-fast velocity of the order of 1% the speed of light. Our main results are the observation of i) a linear polariton dispersion accompanied with diffusion-less motion, ii) flow without resistance when crossing an obstacle, iii) suppression of Rayleigh scattering and iv) splitting into two fluids when the size of the obstacle is comparable with the size of the wavepacket. This work opens the way to the investigation of new phenomenology of out-of-equilibrium condensates.
Dispersion of bulk exciton polaritons in a semiconductor microcavity
Physical Review B, 1996
Dispersion of two-dimensional ͑2D͒ exciton polaritons in a semiconductor microcavity containing bulk excitons in a central layer has been considered using the transfer-matrix technique and Pekar's additional boundary conditions. Solving dispersion equations for TE and TM polarized light modes we have obtained angle-dependent complex self-energies of eigenpolariton states, which have been compared with frequencies of resonant features in the calculated spectra. In TM polarization a pronounced spectral feature associated with the longitudinal polariton mode has been found in the vicinity of the lowest transverse polariton state, so that the 2D-polariton dispersion has a form of double anticrossing in this region. In the strong-coupling regime, the polariton splitting ͑Rabi splitting͒ decreases with an increasing index of the confined polariton state. Splittings between spectral dips exceed strongly Rabi splittings for higher exciton states. ͓S0163-1829͑96͒02343-0͔
Collective fluid dynamics of a polariton condensate in a semiconductor microcavity
Nature, 2009
Semiconductor microcavities offer a unique system to investigate the physics of weakly interacting bosons. Their elementary excitations, polaritons-a mixture of excitons and photons-behave, in the low density limit, as bosons that can undergo a phase transition to a regime characterised by long range coherence 1,2 . Condensates of polaritons have been advocated as candidates for superfluidity 3 ; and the formation of vortices 4 as well as elementary excitations with a linear dispersion 5 are actively sought after. In this work, we have created and set in motion a macroscopically degenerate state of polaritons and let it collide with a variety of defects present in the sample. Our experiments show striking manifestations of a coherent light-matter packet that displays features of a superfluid, although one of a highly unusual character as it involves an out-ofequilibrium dissipative system where it travels at ultra-fast velocity of the order of 1% the speed of light. Our main results are the observation of i) a linear polariton dispersion accompanied with diffusion-less motion, ii) flow without resistance when crossing an obstacle, iii) suppression of Rayleigh scattering and iv) splitting into two fluids when the size of the obstacle is comparable with the size of the wavepacket. This work opens the way to the investigation of new phenomenology of out-of-equilibrium condensates.
Femtosecond dynamics of semiconductor-microcavity polaritons in the nonlinear regime
Solid State Communications, 1996
We have investigated novel femtosecond dynamics of cavity-polaritona in a semiconductor quantum microcavity. When the cavity-polaritons are excited with a strong resonant pump in the nonlinear regime, we observe a reduction of cavitypolariton normal-mode splitting (vacuum Rabi splitting) due to saturation of the excitonic transition. By time-resolving the vacuum Rabi splitting, we observe novel properties of cavity-polaritons, including in-plane momentum relaxation associated with inhomogeneous broadening, and the absence of exciton scattering when the superposition of the cavity-polariton modes corresponds to the photon mode. This coherent dynamics is compared with the off-resonance pump case. In addition, we report no evidence of excitation of higher levels (n > 1) of the Jaynes-Cummings model. Keywords: A. quantum wells A. semiconductor D. electron-electron interaction D. optical properties D. quantum localization D. radiation effect SINCE Weisbuch et al. invoked the cavity-polariton picture of the strongly coupled system involving excitons and photons in their paper on the first observation of the vacuum-field Rabi splitting (VRS) in semiconductor microcavities [l], there has been considerable interest in cavity-polariton dynamics. A cavity-polariton is the normal mode of a system composed of an exciton with well-defined wave vector and a narrow electromagnetic resonance of an optical cavity. In the context of atoms in cavities, the energy difference between the normal modes is known as the vacuum-field Rabi splitting. In the time domain, a short though weak optical pulse can excite nonstationary modes in which the dynamics display a l periodic oscillation corresponding to the transfer of excitation from the exciton to the cavity mode. These temporal oscillations are denoted vacuum-field Rabi oscillations (VRO), and their frequency is given by the VRS. Recent studies of cavity-polaritons include radiation by polaritons [2,3], polariton dispersion [4], and optical nonlinearities measured in four-wave mixing [5]. In the linear regime, we can understand the dynamics of the coupled exciton-cavity modes equivalently in the frameworks of cavity quantum electrodynamics [6-8] or lineardispersion theory [1,8,9]. Both theories successfully explain the VRS and the in-plane momentum conservation obeyed by the coherent cavity-polariton radiation when the exciton-cavity system is weakly excited. In this regime, the Jaynes-Cummings model [lo] becomes equivalent to the linear dispersion of the coupled excitoncavity system [II]. The VRS is independent of light intensity incident on the cavity, since the vacuum-field Rabi frequency exceeds the externally-driven Rabi frequency. The dynamics of cavity-polaritons in the nonlinear 941
Polariton Spinor Interactions in a GaAs-based microcavity
We report on spinor polariton interactions in GaAs based microcavity. This investigation is carried out by means of heterodyne polarized pump-probe spectroscopy. The results reveal the magnitude and the sign of interaction strength between polaritons with parallel and anti-parallel spins. We clearly show the dependence of the attractive and repulsive interaction constants with the cavity detuning. We evidence the strong influence of the biexciton resonance on the attractive interaction strength. Our modelization based on Gross-Pitaevskii equation reproduces the experimental observations. PACS numbers: 78.67. De, 71.36.+c Microcavity exciton polaritons are quasiparticles resulting from the strong coupling between excitons and photons . Polaritons exhibit mutual interactions coming from their excitonic content and light effective mass inherited from the photon. Moreover, the collected photons emitted from the cavity allow to read out the polaritons properties. As a matter of fact, a polariton fluid is an ideal tool for investigating quantum phenomena in solid-state systems. Polariton interactions in semiconductor microcavities play a crucial role in a wide variety of topics ranging from nonlinear optical effects, polariton superfluidity to Bose Einstein condensation. Their quantum coherence properties have been extensively investigated since the observation of polariton parametric processes [2-6]. First signs indicating spontaneous quantum degeneracy of polaritons appeared with the observation of stimulated emission under non-resonant excitation . In 2006, polariton Bose-Einstein condensation was demonstrated for the first time . Since then, many experiments have been performed to assess the superfluidity of polaritons, as well as the observation of full [10] and half quantized vortices, the demonstration of polariton flowing without scattering , and of solitons . The observation of the Bogoliubov excitations has been performed after initial indications of the linearization of the polariton dispersion .
2001
We consider a generalization of the Dicke model. It describes localized, physically separated, saturable excitations, such as excitons bound on impurities, coupled to a single longlived mode of an optical cavity. We consider the thermal equilibrium of the model at a fixed total number of excitons and photons. We find a phase in which both the cavity field and the excitonic polarization are coherent. This phase corresponds to a Bose condensate of cavity polaritons, generalized to allow for the fermionic internal structure of the excitons. It is separated from the normal state by an unusual reentrant phase boundary. We calculate the excitation energies of the model, and hence the optical absorption spectra of the cavity. In the condensed phase the absorption spectrum is gapped. The presence of a gap distinguishes the polariton condensate from the normal state and from a conventional laser, even when the inhomogeneous linewidth of the excitons is so large that there is no observable polariton splitting in the normal state. 71.35.Lk, 71.36.+c, 71.35.Aa, 64.60.Cn
Polariton-polariton interaction constants in microcavities
Physical Review B, 2010
Resonant transmission of light through a microcavity in the strong coupling regime is used to estimate the strength of the interaction between polaritons with parallel ͑␣ 1 ͒ or antiparallel ͑␣ 2 ͒ spins. The ratio ␣ 2 / ␣ 1 is found to be strongly dependent on the detuning between exciton and photon modes. From negative to zero detuning it changes from about 0 to less than −1. Our observations indicate that at certain conditions the polaritons might rather condense in the real space than form a Bose-Einstein condensate. We analyze theoretically different mechanisms of polariton-polariton interaction including the mean-field electrostatic interaction, the direct exchange interaction, the Van-der-Waals interaction and the indirect exchange interaction via dark exciton and biexciton states.
Energy relaxation of exciton-polariton condensates in quasi-one-dimensional microcavities
Physical Review B, 2013
We present a time-resolved study of energy relaxation and trapping dynamics of polariton condensates in a semiconductor microcavity ridge. The combination of two non-resonant, pulsed laser sources in a GaAs ridge-shaped microcavity gives rise to profuse quantum phenomena where the repulsive potentials created by the lasers allow the modulation and control of the polariton flow. We analyze in detail the dependence of the dynamics on the power of both lasers and determine the optimum conditions for realizing an all-optical polariton condensate transistor switch. The experimental results are interpreted in the light of simulations based on a generalized Gross-Pitaevskii equation, including incoherent pumping, decay and energy relaxation within the condensate.