Coherent control of polariton parametric scattering in semiconductor microcavities

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k=0, even for delays much longer than the pulse width. The control of a large population at k=0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the scattering get faster. Just above threshold the parametric scattering process shows unexpected long coherence times, whereas when pump power is risen the contrast decays due to a significant pump reservoir depletion. The weak pulses at normal incidence control the whole angular emission pattern of the microcavity.     

Spatial coherence of a polariton condensate

We perform Young's double-slit experiment to study the spatial coherence properties of a two-dimensional dynamic condensate of semiconductor microcavity polaritons. The coherence length of the system is measured as a function of the pump rate, which confirms a spontaneous buildup of macroscopic coherence in the condensed phase. An independent measurement reveals that the position and momentum uncertainty product of the condensate is close to the Heisenberg limit. An experimental realization of such a minimum uncertainty wave packet of the polariton condensate opens a door to coherent matter-wave phenomena such as Josephson oscillation, superfluidity, and solitons in solid state condensate systems.     

Adiabatic Raman polariton in a Bose condensate

The Raman interaction of optical fields with a Bose condensate is studied in the adiabatic regime. A superposition of operators is found — one annihilating an atom in a metastable state and the other annihilating a photon in resonance with a transition from the ground state to an excited state — which is an adiabatic invariant of the problem (Raman polariton). Possible applications for Bose-condensate diagnostics and development of atomic lasers are proposed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 473–477 (10 October 1996)     

Spontaneous pattern formation in a polariton condensate

Exciton-polariton condensation can be regarded as a self-organization phenomenon, where phase ordering is established among particles in the system. In such condensed systems, further ordering can occur in the particle density distribution, under particular experimental conditions. In this work we report on spontaneous pattern formation in a polariton condensate under nonresonant optical pumping. The slightly elliptical ring-shaped excitation laser that we employ forces condensation to occur into a single-energy state with periodic boundary conditions, giving rise to a multilobe standing-wave patterned state.     

Room-temperature polariton lasing in semiconductor microcavities

We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 microJ cm-2, 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum-well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/-5 degrees and spatial size around 5 microm.     

Soliton excitations in a polariton condensate with defects

To study soliton excitations in a polariton condensate with defects, we use the Gross-Pitaevskii equation and its hydrodynamic form. An extra term is added to take into account the non-equilibrium nature of the polariton condensate and the presence of defects. The reductive perturbation method transforms these hydrodynamic equations into a modified Korteweg-de Vries equation in the long wavelength limit. We linearize this equation and study the soliton linear excitations.We give an analytic expression of traveling excitations using the variation of constants method. In the more general form,we show numerically that the excitations are oscillations, i.e., the amplitude and the width of the dark soliton oscillate simultaneously but in an opposite way.     

Two-photon scattering by a driven three-level emitter in a one-dimensional waveguide and electromagnetically induced transparency

We study correlated two-photon transport in a (quasi-)one-dimensional photonic waveguide coupled to a three-level Λ-type emitter driven by a classical light field. Two-photon correlation is much stronger in the waveguide for a driven three-level emitter (3LE) than a two-level emitter. The driven 3LE waveguide shows electromagnetically induced transparency (EIT), and we investigate the scaling of EIT for one and two photons. We show that the two transmitted photons are bunched together at any distance separation when energy of the incident photons meets "two-photon resonance" criterion for EIT.     

Drag in a resonantly driven polariton fluid

We study the linear response of a coherently driven polariton fluid in the pump-only configuration scattering against a point-like defect and evaluate analytically the drag force exerted by the fluid on the defect. When the system is excited near the bottom of the lower polariton dispersion, the sign of the interaction-renormalised pump detuning classifies the collective excitation spectra into three different categories (Ciuti and Carusotto 2005 Phys. Status Solidi b 242 2224): linear for zero, diffusive-like for positive and gapped for negative detuning. We show that both cases of zero and positive detuning share a qualitatively similar crossover of the drag force from the subsonic to the supersonic regime as a function of the fluid velocity, with a critical velocity given by the speed of sound found for the linear regime. In contrast, for gapped spectra, we find that the critical velocity exceeds the speed of sound. In all cases, the residual drag force in the subcritical regime depends on the polariton lifetime only. Also, well below the critical velocity, the drag force varies linearly with the polariton lifetime, in agreement with previous work (Cancellieri et?al 2010 Phys. Rev. B 82 224512), where the drag was determined numerically for a finite-size defect.     

A parametric study of radiative transfer with anisotropic scattering in a one-dimensional system

Radiative heat transfer in an absorbing, emitting, anistropically-scattering, one-dimensional medium is analyzed. Unlike many of the existing works, the present analysis does not require a known temperature distribution within the medium. Assuming a model of linear anistropic scattering, the transfer equation and the energy equation are solved simultaneously by utilizing a recently developed successive approximation technique. Closed-form approximate solutions and accurate higher-order results are both presented. Calculations show that the relative importance of the anistropic scattering effect generally decreases with decreasing wall emissivity and decreasing optical thickness. For radiative equilibrium without internal heat generation, it is demonstrated that the anistropic-scattering heat-transfer results can be approximated quite adequately by the isotropic-scattering result with the introduction of the concept of an effective optical thickness. For media with internal heat generation, an interesting effect of the scattering albedo is observed. It is established that, in the limit of a large scattering albedo, the temperature of the medium approaches a constant value that is independent of anistropic-scattering effects and wall emissivity. The exact limiting expressions for the temperature and apparent emissivity of an isothermal slab are found.     

Oblique solitons generated by the flow of a polariton condensate past an obstacle

The formation of oblique solitons in a polariton condensate flowing past an obstacle is considered. Because of the finite lifetime of polaritons, the condensate flow is inhomogeneous, which leads to a significant modification of the conditions necessary for the generation of oblique solitons as compared to the conditions established earlier for the flow of an atomic condensate. In particular, it is established that oblique solitons in the polariton case can be generated by a subsonic flow of the condensate in agreement with the results of recent experiments [9]. The geometric shape and other parameters of oblique solitons are analytically calculated using a model based on the nonlinear Schr?dinger equation with damping, and the analytical results are confirmed by numerical simulations.     

Kinetics of stimulated polariton scattering in planar microcavities: evidence for a dynamically self-organized optical parametric oscillator

Strong temporal hysteresis effects in the population kinetics of pumped and scattered lower polaritons (LPs) have been observed in a planar semiconductor microcavity under a nanosecond-long pulsed resonant excitation (by frequency and angle) near the inflection point of the LPs' dispersion. The hysteresis loops have a complicated shape due to the interplay of two instabilities. The self-instability (bistability) of the nonlinear pumped LP is accompanied by a strong parametric instability which causes an explosive growth of the scattered LPs' population over a wide range of wave vectors. Finally, after a 30-500 ps period, a three-mode scattering pattern forms, thereby demonstrating a dynamically self-organized regime of the optical parametric oscillator. Stability is maintained by the presence of numerous weak "above-condensate" modes; the whole system therefore appears to be highly correlated.     

Microcavity polariton scattering probed by coherent control experiments

We present coherent control experiments which simultaneously probe both the coherence and the population dynamics of the exciton–photon polariton states in a semiconductor microcavity. The coherent manipulation of either the spin orientation or the density of polaritons is demonstrated leading to the measurement of the optical dephasing time. The polariton scattering by acoustical phonons or by mutual collision processes are investigated by a simultaneous measurement of both the optical dephasing time T₂and the decay time T₁of the radiant states. These results clearly evidence a quenching of the different scattering processes at resonance.     

Surface plasmon polariton scattering by small ellipsoid particles

Scattering of surface plasmon polaritons (SPP’s) by small ellipsoid particles placed near a dielectric–metal interface is theoretically considered. Using the Green’s function formalism and the dipole approximation, we consider the differential and total scattering cross-sections associated with the SPP-to-SPP scattering as well as with the SPP scattering into waves propagating away from the interface, analyzing the influence of system parameters. As an example, scattering cross-sections of differently shaped gold spheroid particles placed near an air–gold interface are evaluated at the light wavelength of 800 nm. It is shown that the differential and total cross-sections depend strongly upon the particle-to-surface distance, the ratio between the major and minor axes and their orientation with respect to both the interface and the direction of SPP incidence. Implications of the obtained results to the design of SPP micro-optical components are also discussed.     

Intrinsic decoherence mechanisms in the microcavity polariton condensate

The fundamental mechanisms which control the phase coherence of the polariton Bose-Einstein condensate (BEC) are determined. It is shown that the combination of number fluctuations and interactions leads to decoherence with a characteristic Gaussian decay of the first-order correlation function. This line shape, and the long decay times ( approximately 150 ps) of both first- and second-order correlation functions, are explained quantitatively by a quantum-optical model which takes into account interactions, fluctuations, and gain and loss in the system. Interaction limited coherence times of this type have been predicted for atomic BECs, but are yet to be observed experimentally.     

Second-order time correlations within a polariton Bose-Einstein condensate in a CdTe microcavity

Second-order time correlations of polaritons have been measured across the condensation threshold in a CdTe microcavity. The onset of Bose-Einstein condensation is marked by the disappearance of photon bunching, demonstrating the transition from a thermal-like state to a coherent state. Coherence is, however, degraded with increasing polariton density, most probably as a result of self-interaction within the condensate and scatterings with noncondensed excitons and polaritons. Such behavior clearly differentiates polariton Bose condensation from photon lasing.     

Raman scattering by the upper branch polariton in ZnO

The first observation of Raman scattering from the upper branch polariton in a semiconductor is reported. The significant reduction in collecting solid angle is the main cause that allows for this observation. The experimental polariton dispersion relation ω(K) can only be accounted for when dispersion is taken into consideration.     

High order harmonics driven by a self-phase-stabilized IR parametric source

We analyze the emission of coherent XUV radiation in gaseous targets by high-order harmonics of tunable infrared (1.4–1.6 μm) laser pulses generated by a parametric source. As noticeable application, we show that a continuous spectrum spanning the 40–200 eV region can be efficiently generated by mixing the infrared pulses with visible pulses at 800 nm. These results open new perspectives for the extension of attosecond physics towards the soft-X region and for the investigation of atoms and molecules on a broader range of photon energies with respect to the state of the art.     

Controllability of shock waves in one-dimensional polariton condensates

In one-dimensional incoherent pumped exciton–polariton condensates, we realize the generation and control of supersonic shock waves. By choosing a suitable initial input wave, we obtain the region of existence of various shock waves as a function of the phase of the initial wave, the coefficient of polariton interaction, the coefficient of the interaction between polariton and reservoir and the condensation rate and intensity of pumping. Using these results, we discuss the effect of different pa...     

Homopolar oscillating-disc dynamo driven by parametric resonance

We use a simple model of Bullard-type disc dynamo, in which the disc rotation rate is subject to harmonic oscillations, to analyze the generation of magnetic field by the parametric resonance mechanism. The problem is governed by a damped Mathieu equation. The Floquet exponents, which define the magnetic field growth rates, are calculated depending on the amplitude and frequency of the oscillations. Firstly, we show that the dynamo can be excited at significantly subcritical disc rotation rate when the latter is subject to harmonic oscillations with a certain frequency. Secondly, at supercritical mean rotation rates, the dynamo can also be suppressed but only in narrow frequency bands and at sufficiently large oscillation amplitudes.     

Collisional decay of a strongly driven Bose-Einstein condensate

We study the collisional decay of a strongly driven Bose-Einstein condensate oscillating between two momentum modes. The resulting products of the decay are found to strongly deviate from the usual s-wave halo. Using a stochastically seeded classical field method we simulate the collisional manifold. These results are also explained by a model of colliding Bloch states.